mm-1037

> Recall that (x,s)-space is a poor man¹s version of string
space
> (with the advantage of being Žnite-dimensional and thus more
> tractable). A 2-connection in ordinary x-space corresponds
to a
> 1-connection A_i(x,s) in string space. For clarity, I¹ll
write out
> arguments and indices explicitly. The 1-connection
transforms in
> the usual ways under gauge transformations in (x,s)-space
and
> diffeomorphisms in x-space, extended to (x,s)-space by
requiring
> that s transforms as a vector. This makes the 2-form
curvature
> F_ij(x,s) = d_i A_j(x,s) - d_j A_i(x,s) + [A_i(x,s),
A_j(x,s)]
> (d_i = d/dx^i) well-deŽned, and we can use it to write down
a
> nice invariant action which generalizes Yang-Mills.
When you go to the continuum limit with this you see that the
surface
holonomy this induces is independent of the path in loop
space or path
space
(what you call string space) precisely if your A (which is
usually called
B)
is abelian (Žrst noticed by C. Teitelboim in Phys. Lett. B
167 (1986) 63).
You can then augment your connection by the adjoint action of
a target
space
1-form as in hep-th/9710147, hep-th/0207017, hep-th/0407122
(which is
implied by gauge transformations on loop space) and Žnd that
now the
surface holonomy is independent of the path in loop space
precisely if the
non-abelian 1-form and the 2-form together satisfy a certain
condition,
which is precisely the condition that these forms deŽne a weak
2-connection, i.e. a functor from the strict 2-groupoid of
bigons to a
sesqui-group. A special case of this is a slightly stromger
condition which
makes this a strict 2-connection (hep-th/0309173), i.e. a
functor to a
strict 2-group.
The objects on loop space can be shown to be well-deŽned
precisely if the
background 1+2 form gauge Želds satisfy certain equations of
motion.
For
the case B=0 this is shown in hep-th/0312260 for the
non-abelian and in
hep-th/9909027 and JHEP 04 (2000) 023 for the abelian case.
This easily
generalizes to non-abelian and nontrivial B, as discussed in
hep-th/0407122.
===
Subject: Re: Operator product question
> ... <T_{zz} T_{bar w bar w} = - (pi c/ 12)
partial_zpartial_{bar z}delta^2(z-w) +
...
I know a different CFT in which you can realize this formula
easily.
Take the linear dilaton CFT, with the term proportional to
Vpartialpartial X included in T_{zz}. You know that this
contributes
something like 6 V^2alpha¹ to the central charge, but on the
other
hand, you can also see that it contributes your desired
second (mixed)
derivative of the two-dimensional delta function to the
correlator of
T_{zz} and T_{bar wbar w} (fourth derivative, the 2+2 mixed
one, of
the logarithm), and I believe that the coefŽcient will match
(the
factors of pi and 3 work out correctly; I have not checked
the powers
of two and the sign). Well, I still do not know how to get
this nice
result from the free boson, but at least one CFT seems to
give the
formally derived contact term explicitly.
Best wishes, Lubos
===
Subject: Re: SFT & non-perturbative degrees of freedom
Lubos Motl <motl@feynman.harvard.edu> schrieb im Newsbeitrag
> All these reasons led the people to focus on the open
string Želd theory
> whose action can be well-deŽned - e.g. the cubic
(polynomial) Witten¹s
> action; it is enough to get the full amplitudes and cover
the full
Riemann
> surface moduli spaces. Can one see all physics of string
theory in it?
> Well, the Žrst problem are the closed string states. They
can be seen as
> poles in open string scattering, but as far as I know, no
one has made a
> convincing construction of the closed strings as composites
of the open
> string Želds so far. The understanding of the closed
strings would have
> to improve a lot so that one could also construct
non-trivial geometric
> conŽgurations including NS21-branes (or NS5-branes) etc. in
open SFT.
What looks plausible and weird at the same time is that in the
nonperturbative vacuum of OSFT (as it is sometimes called),
meaning the
point where the tachyon is sitting in its minimum and the D25
brane has
completely decayed, the BRST operator of the OSFT with that
background is
pure ghost and has trivial cohomology. On the one hand side
this is
plausible, because at this point the open strings must have
disappeared, so
that it makes sense that no non-trivial physical states are
left. On the
other hand *something* should be left, namely physical states
of closed
strings. Where are they in this picture? I have once seen a
paper arguing
how these might arise from that pure-ghost BRST operator, but
I didn¹t
understand the construction and forget which paper that was,
unfortunately.
> Another question are the D-branes. Using the modern
perspective, the open
> strings themselves describe dynamics of a spacetime Žlling
D-brane.
Sen¹s
> insights made it expected that one can construct the lower
dimensional
> branes as classical solutions of open string Želd theory.
And this has been checked in many examples, hasn¹t it?
> I think that its internal dynamics is itself target space
dynamics of
> some other string theory; I have the N=2 and N=(2,1) string
in mind.
That¹s one of the most intriguing things that I have ever
heard of, which
was when you Žrst told me about it at the SCT
http://golem.ph.utexas.edu/string/archives/000265.html#
c000386.
It seems to imply that what one needs is a Želd theory of
target space
theories (as opposed to an ordinary target space Želd theory
,-) of the
N=(2,1) string. It would automatically contain the ordinary
string as well
as membrane degrees of freedom and the like.
Hm, so maybe the ordinary cubic vertex of OSFT must be
replaced by some
sort
of vertex of objects living in a delPezzo or something?
> ... One more comment. There have been some Japanese papers
that studied
> the behavior of the boundary states under the closed-string
> Kyoto-group-like SFT star product; the boundary states act
as projectors,
> roughly speaking. This sort of thinking, even though it is
formal, looks
> like an important step towards obtaining the
non-perturbative
> generalization of CFT mentioned above. Today, our
consistency
requirements
> for closed strings and open strings follow similar logic,
but technically
> they are different.
So maybe one can make a change of variables from string
degrees of freedom
to brane-degrees of freedom in the SFT formulaiton: Usually
the string
Želd
Phi is expanded in terms of worldhseet oscilllation with
respect to the
ordinary worldsheet vacuum. On the other hand, as you point
out, there are
string Želds Phi, the boundary states, which are far from
that worldsheet
vacuum and describe offshell states that encode various
D-branes. Maybe
there are enough of these boundary states that one can expand
any other
string Želd in terms of them? hat would replace the ordinary
expansion in
terms of string oscialltions by something like an expansion
in terms of
D-brane states. The question would be: Do the boundary states
of SFT form a
complete set in an appropriate sense?
I think this might even be true. To me the fact that boundary
states which
encode a space-Žlling brane with arbitrary gauge Želd
excitations are
just
a recombination of DDF states hints at precisely such a
reformulation.
> This is a sort of bootstrap thinking, but maybe not so
impossible - it
may
> be just a generalization of CFTs.
BTW, your exposition has generated some reactions over here:
http://www.math.columbia.edu/~woit/blog/archives/000080.html .
===
Subject: Deep questions in string cosmology
The science journalist Ruediger Vaas has posted to the String
Coffee Table
http://golem.ph.utexas.edu/string/archives/000424.html#c001571
in (string) cosmology, emphasizing the notion of the
beginning of time
in
cosmology as well as the very nature of space and time.
If anyone feels like thinking about philosophical questions
on the basis of
current ideas in cosmology and string theory he or she will
certainly enjoy
In particular, Ruediger is challenging string theorists to
provide him with
demonstrations that spacetime is a secondary and derived
concept in string
theory and he is wondering about the question if and in which
sense strings
can be considered as being elementary.
Interesting replies have a good chance of being incorporated
in future
German science journal Bild der Wissenschaft
http://bdw.wissenschaft.de/bdw/heft/liste.html .
===
Subject: Re: Background Independence
> [Moderator¹s note: Well, if there are massless D3-branes,
then the
> CFT breaks down. The CFT can perturbatively treat the
perturbative
> string states only, and they are too light and unable to
change
> the topology too much. Perturbative string theory is only
OK if the
> states that it neglects - such as D-branes - are heavy or
otherwise
> decoupled. It¹s not just a matter of calculational
> complexity: it is also difŽcult physically to change the
topology
> of space. LM]
I¹m not sure if you¹re disagreeing with Rufus as I¹ve quoted
him in the
post above, or just with my interpretation of what he was
saying....
Also, I thought you said the D3-branes in the target space
can be
described by adding a boundary to the world sheet CFT. Is
this what you
mean by break down?
[Moderator¹s note: No. InŽnitely extended D3-branes or
D3-branes wrapped
on
Žnite volumes are, indeed, represented by adding all possible
worldsheets that can also have the boundaries with the
boundary
conditions associated with these D3-branes. The conformal
Želd theory
is generalized, according to Polchinski¹s recipe, and it
accounts
for the physics of the original background plus the D3-branes.
However, I was talking about *massless* D3-branes. If you
consider
a topology change similar to the conifold transition, you
will Žnd out
that there are 3-dimensional cycles at the conifold point -
the singular
point in the moduli space where the manifold pinches off.
D3-branes can
be wrapped on these vanishing cycles (3-dimensional
submanifolds of
vanishing volume), and because their total mass is
proportional to the
volume and the volume goes to zero, these D3-branes are
massless.
That¹s a disaster for the conformal Želd theory. The
well-behaved,
Žnite-mass D3-branes can be represented by boundaries of the
worldsheets, and the worldsheets with too many boundaries
become
increasingly irrelevant. However, if the D3-branes are
massless,
the worldsheets with very many boundaries cannot be neglected
- in
fact, they are at least as important as the worldsheet with a
few
boundaries. Consequently, the sum over Riemann surfaces with
boundaries
does not converge at all, and you can¹t get any Žnite results
out of
it.
By breaking down in physics, we always mean that the theory
does not work at all anymore, and your calculations lead to
nonsensical
(divergent) results. This is what happens with a CFT if some
D-branes
become massless. More generally, this breakdown occurs for any
as soon as you try to describe a situation in which some other
always mean a disaster for your original description.
You may object by saying that the D3-branes *were* accounted
for because
we *wanted* to add the boundaries. That might have been true,
but they
were not treated as *perturbative* objects but rather as
solitons
(a generalization of the magnetic monopole; a classical
solution
interpreted as a very heavy object). This solitonic
description is not
good enough if they are light; if the D3-branes become light,
i.e. if
the volume of the 3-cycle shrinks to zero, the D3-branes
should be
considered on equal footing with the fundamental strings,
which is
certainly not what the conformal Želd theory is doing.
However, this
democratic treatment *can* be achieved if we use a spacetime
effective
Želd theory - with light perturbative string states *and* the
new Želds
arising from the light/massless D3-branes. This strategy was
chosen
by Andy Strominger, and he was the Žrst one who understood
that the
existence of D3-branes exactly accounts for all singularities
seen in
the Želd theoretical description. He found out that the full
string
theory, including all the predicted D3-branes etc., is smooth
and
non-singular. A week later, he and Brian Greene and David
Morrison
extended this fact and showed that topology can be changed at
this point.
Rufus understand that the pure conformal Želd theory is
meaningless
at the point where the D3-branes become massless, i.e. at the
very
moment when the topology change occurs. LM]
-------------------------------------------------------------
-----------
This post submitted through the LaTeX-enabled
physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=38812#post316269
===
Subject: Re: T-dual coordinate
> [Moderator¹s note: I thought you wanted closed strings -
see page 249
> (middle) and 250 of Polchinski I for the description of the
shift
> between velocities and momenta. The situation of open
strings is
> related, but you should keep in mind that the open strings
can end
> on various D-branes, and the distance between the D-branes
is T-dual
> to the Wilson line that breaks U(2) to U(1)^2, for example.
One must
> also realize that B+F is the only physical combination
because the
> electromagnetic potential A living on the brane transforms
under the
> B-Želd¹s gauge invariance, Bto B+dlambda, Ato A-lambda. LM]
always considering open strings with no chan-paton factors,
and the
equation I have in the earlier posts:
X¹^9(sigma=pi) - X¹^9(sigma=0) = pi*(n/R + p^1)
is supposed to be the set of possible lengths of an open
string
stretching between two copies of the same D-brane, but with
an unwanted
dependence on p^1. I¹ve taken a step too far though, as it
should be:
X¹^9(sigma=pi) - X¹^9(sigma=0) = pi*(G_{9,9}p^9 + G_{1,9}p^1)
I was then (foolishly) assuming p^9 = n/R, but I think really
it should
be (G_{9,9}p^9 + G_{1,9}p^1)=n/R that¹s quantized, I guess.
Then you
have the usual equation for the length of the string
stretching between
D-branes, with no p^1 dependence.
So it was a red herring, really - at least I think so, now.
The
classical sigma model calculation still seems like a neat way
to see
the transformation of all the background Želds, though, and
the more
general relation between X and X¹ with background Želds
turned on.
-------------------------------------------------------------
-----------
This post submitted through the LaTeX-enabled
physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=41365#post316907
===
Subject: Re: Self-dual lattices
everything above. I hadn¹t realised that the enhanced gauge
symmetry
can occur when Lambda is not necessarily self-dual, and
presumably
even when Lambda is self-dual there may be no enhanced gauge
symmetry. (I guess the examples I¹d seen incorrectly gave me
the
impression that self-duality of Lambda was associated with a
non-abelian symmetry).
[Moderator¹s note: Yes, the example with non-self-dual
lattices and
extended symmetry is given in the previous posting - a
self-dual
radius of X9 and a generic radius of X8. On the other hand,
type
II string theories do not have any enhanced non-Abelian
symmetry even
at the special value of the radii. LM]
While I expected the proposition at the top of this thread to
be too
strong to be true, somehow there must still be a relation
between
every lattice giving rise to extra massless states, and the
appropriate Lie group? This connection still seems a bit
mysterious
to me.
[Moderator¹s note: I am not exactly sure why. Write down a
Yang-Mills
theory with a general gauge group and study its perturbative
spectrum.
You will Žnd the gauge bosons. If you classify them according
to the
U(1)^l charges - under the Cartan subalgebra - the charges
that will
appear will be exactly the roots of the Lie algebra. A string
theory
can describe the same Yang-Mills theory at low energies if
its spectrum -
the spectrum of possible vibrating strings - reproduces the
required
spectrum of the gluons. The existence and properties of gauge
bosons
is exactly what contains the information about the gauge
group. There
and they *deŽne* what the gauge group is. LM]
-------------------------------------------------------------
-----------
This post submitted through the LaTeX-enabled
physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=41595#post316260
===
Subject: Re: Self-dual lattices
Sorry, I¹ve also just realised that you imply that the
enhanced gauge
symmetry can occur when Lambda is not necessarily
self-dual...and
perhaps also that there may be no enhanced symmetry even when
Lambda
is self-dual. So probably there is no reason to expect a
connection
between the gauge groups and the self-dual lattices....
[Moderator¹s note: Right. For example, the enhanced symmetry
appears if
the radius of X9 is T-self-dual, but the radius of X8 can be
anything.
The lattice of allowed momenta (p8,p9) is not self-dual,
because X8
breaks it, but nevertheless there will be new gauge bosons and
non-Abelian symmetry. LM]
-------------------------------------------------------------
-----------
This post submitted through the LaTeX-enabled
physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=41595#post316274
id 1C5mu8-0007wN-51
===
Subject: I¹ve got a question...
I would¹ve posted this question in the chemistry newsgroup
but the
people in there seem like idiots and I fear it would never get
answered. Heat is deŽned as the vibration of molecules right?
Well how
does heat then travels through a vacuum?
by mailbox4.ucsd.edu (8.13.1/8.13.1) with ESMTP id
i8DDnNft049821
===
Subject: Re: I¹ve got a question...
X-Spam-Status: No, hits=-3.4 required=5.0
RCVD_IN_ORBS,REFERENCES
version=2.55
> I would¹ve posted this question in the chemistry newsgroup
but the
> people in there seem like idiots and I fear it would never
get
> answered. Heat is deŽned as the vibration of molecules
right? Well how
> does heat then travels through a vacuum?
Radiation.
Jeff
--
Remove icky phrase from email address to get a valid address.
id 1C6Tm8-000LuP-C8
CC: sci-space-science@moderators.isc.org
===
Subject: Re: I¹ve got a question...
> Heat is deŽned as the vibration of molecules right?
No. Heat is the average randomized kinetic energy per volume.
Vibration of molecules is one such form of energy, but there
are many
others.
> Well how does heat then travels through a vacuum?
It doesn¹t. Something else, say light, does travel through the
vacuum. When it arrives it reacts locally, say with the dirt,
and is
converted into heat.
Consider how your stove works. You apply electricity and out
comes
heat. Electricity is not hot, in fact it is rather ordered,
and thus
very cool. So electricity is not heat, nor is light, nor are
lots of
things that can be _turned_into_ heat.
Maury
id 1C6PXR-000ISg-1p
with ESMTP id EAA24561 for
<sci-space-science@moderators.isc.org>;
===
Subject: Re: I¹ve got a question...
As all radiating energy from the spectrum do.
id 1C60vt-0006WM-00
for <sci-space-science@moderators.isc.org>;
for <sci-space-science@moderators.isc.org>;
===
Subject: Re: I¹ve got a question...
>I would¹ve posted this question in the chemistry newsgroup
but the
>people in there seem like idiots and I fear it would never
get
>answered. Heat is deŽned as the vibration of molecules
right? Well how
>does heat then travels through a vacuum?
Heat, thus deŽned, doesn¹t. But energy can be converted from
one
form to another. Electromagnetic radiation and the kinetic
energy of
vibrate. Kind of like the cue ball hitting the pack in pool.
--
R.G. Stumpy Marsh.
id 1C5vv9-0000De-00
with ESMTP id <0I3U009EAPT77380@l-daemon> for
with ESMTP id <0I3U00F18PT2UG@l-daemon> for
===
Subject: Re: I¹ve got a question...
X-Complaints-to: abuse@shaw.ca
MIME-version: 1.0
X-NNTP-posting-host: 24.71.223.147
>I would¹ve posted this question in the chemistry newsgroup
but the
>people in there seem like idiots and I fear it would never
get
>answered. Heat is deŽned as the vibration of molecules
right? Well how
>does heat then travels through a vacuum?
As I understand it, It doesn¹t. The Vibrating molecules
produce
radiation that travels across the vacuum. This radiation is
then
absorbed by molecules at the other end, causing them to
vibrate.
Only two things are inŽnite, the universe and human
stupidity, and I¹m not
sure about the former.
Albert Einstein (1879 - 1955)
===
Subject: Re: I¹ve got a question...
Why do you think so?
Photons travel carrying energy but not heat.
Best wishes,
Alexander Pavlik
by mailbox5.ucsd.edu (8.13.1/8.13.1) with ESMTP id
i8ALX1nN080873
===
Subject: Re: I¹ve got a question...
> I would¹ve posted this question in the chemistry newsgroup
but the
> people in there seem like idiots and I fear it would never
get
> answered. Heat is deŽned as the vibration of molecules
right? Well how
> does heat then travels through a vacuum?
infra-red electromagnetic waves
- nate
by mailbox10.ucsd.edu (8.13.1/8.13.1) with ESMTP id
i8ANwOjL024543
===
Subject: Re: intelligent question
>In space nobody can hear you scream.
The acoustic waves really does not spread in space, because
of their
nature.
These waves are the case of trasmitting of impulses from one
layer of
molecules of air (or atoms in atomic grid ) to the next one
in direction of
spreading of the wave.
But when you perform the scream into electromagnetic waves,
amplify and
transmit them it will be possible to hear the scream in very
huge
distances in space...
(envelope-from news@gnilink.net)
===
Subject: Another question
I just Žnished reading Brian Greene¹s The Elegant
Universe. The section in chapter 15 titled What are
Space and Time, Really, and can we do without them?
suggests in my mind a tantalizing question:
to the graviton) which deŽnes three dimensional space?
Any comments on this would be appreciated.
===
Subject: China girl Žnd pen pal
<!DOCTYPE HTML PUBLIC -//W3C//DTD HTML 4.0 Transitional//EN>
<HTML><HEAD>
<META content=MSHTML 6.00.2800.1276 name=GENERATOR>
<STYLE></STYLE>
</HEAD><FONT face=Arial><FONT size=2>
<BODY>
<DIV>Send email to gzgimsun@163.net or</DIV>
<DIV>&nbsp;</DIV>
Call +86 13802741877 Law Yau.<BR><BR>
<DIV><IMG alt=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
hspace=0
src=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
align=baseline
border=0></DIV></BODY></HTML></FONT></FONT>
===
Subject: New Žndings cast doubt on race isn¹t real claim
For years, mainstream scientists have said there are no real
racial
differences among people. Race is purely a social construct
-- in other
words, it¹s imaginary, some have argued.
But two new studies raise doubts about a key calculation on
which this
argument rests.This calculation, often cited publicly by
world-renowned
geneticists, is that all humans are more than 99.9 percent
genetically
identical.
http://www.world-science.net/exclusives/040908_racefrm
===
Subject: Re: New Žndings cast doubt on race isn¹t real claim
It must depend on what you mean by Œreal¹ and Œrace¹. For a
start, there
are
black and white people. Are they the same race? Not in my
book.
Rob Graham
===
Subject: First-ever photo of planet outside our solar system?
http://www.world-science.net/othernews/040910_planetfrm.htm
===
Subject: Bad Thinking log
This is an invitation to the Atheist Historian¹s Log on Bad
Thinking.
http://atheisthistorian.org/study/badthinking.htm
Hope to see you there!
===
Subject: Re: MY SISTER NAKED IN SHOWER
The man named in a disputed memo as exerting pressure to
sugarcoat
George
W. Bush¹s military record left the Texas Air National Guard a
year and a
half before the memo supposedly was written, his service
record shows.
An order obtained by The Dallas Morning News shows that Col.
Walter
Buck
Staudt was honorably discharged March 1, 1972. CBS News
reported this week
that a memo in which Staudt was described as interfering with
ofŽcers¹
negative evaluations of the future president¹s service was
dated Aug. 18,
1973.
That added to mounting questions about the authenticity of
documents that
seem to suggest Bush sought special treatment as a pilot,
failed to carry
out a superior¹s order to undergo a physical exam and was
suspended from
žying for failing to meet Air National Guard standards.
Staudt, who lives in New Braunfels, Texas, did not return
calls seeking
comment. His discharge paper was among documents obtained by
The Morning
News from ofŽcial sources during 1999 research into Bush¹s
Guard record.
A CBS staffer stood by the story, suggesting Staudt could
have continued to
exert inžuence over Guard ofŽcials. But a former high-ranking
Guard
ofŽcial disputed that, saying retirement would have left
Staudt powerless.
Authenticity of the memo and three others included in
Wednesday¹s 60
Minutes report came in for heavy criticism yesterday,
prompting an
unusual,
on-air defense of the original work. Experts on typography
said the memos
appeared to have been computer-drafted on equipment not
available at the
time.
Jerry Killian, who died in 1984, have said it wasn¹t his
nature to keep
detailed personal notes.
In its news broadcast yesterday, CBS said the documents were
supported by
both unnamed witnesses and others, including document
examiners.
CBS anchor Dan Rather earlier told The Dallas Morning News
that he had
heard
nothing to make him question the legitimacy of the memos. He
attributed the
backlash to partisan politics and competitive journalism.
This story is true. The questions we raised about
then-Lieutenant Bush¹s
National Guard service are serious and legitimate, he said.
Until and
unless someone shows me deŽnitive proof that they are not, I
don¹t see any
reason to carry on a conversation with the professional rumor
mill.
The Washington Post quoted Rather as saying CBS had talked to
two people
who
worked with Killian - his superior, retired Maj. Gen. Bobby
Hodges, and his
administrative assistant Robert Strong - and both described
the memos as
consistent with what they knew of Killian. Hodges, who told
CBS he was
familiar with the documents, is an avid Bush supporter and it
took a
lot
for him to speak the truth, the Post quoted Rather as saying.
The Los Angeles Times, however, later quoted Hodges as saying
that he
believed the memos from Killian were not real. A CBS news
executive
conŽrmed that Hodges had changed his story.
Rather¹s interview with The Morning News concluded before the
newspaper
determined the date of Staudt¹s departure, but a CBS staffer
with extensive
knowledge of the story said later that the departure doesn¹t
derail the
retired, the staffer said, speaking on condition of
anonymity. He was a
very bullying type, and that could have continued.
In the 60 Minutes report, Rather said of the memo¹s contents:
Killian
says Col. Buck Staudt, the man in charge of the Texas Air
National Guard,
is
putting on pressure to Œsugarcoat¹ an evaluation of Lt. Bush.
Staudt was the person Bush initially contacted about Guard
service, and he
was the group commander at Ellington Air Force Base in
Houston when Bush
arrived there to žy an F-102 jet. He transferred later to
Austin, where he
served as chief of staff for the Air National Guard.
message today from group regarding Bush¹s (evaluation) and
Staudt is
pushing
to sugarcoat it.
It continues: Austin is not happy either.
The CBS staffer said the memo appears to recognize that
Staudt has retired,
since it differentiates between his displeasure and that of
Austin, where
he
served his Žnal Guard stint.
But another Texas Air National Guard ofŽcial who served in
that period
said
the memo appears to wrongly associate Staudt with his group
command in
Houston, and - based on that mistake - the memo distinguishes
his views
from
that of the Austin Guard.
Retired Col. Earl Lively, director of Air National Guard
operations for the
state headquarters during 1972 and 1973, said Staudt wasn¹t
on the
scene
after retirement, and that CBS¹ remote-bullying thesis makes
no sense.
He couldn¹t bully them. He wasn¹t in the Guard, Lively said.
He
couldn¹t
affect their promotions. Once you¹re gone from the Guard, you
don¹t have
any
authority.
Bush has not commented publicly about the CBS report, and
aides say his
honorable discharge proves he fulŽlled his obligations.
begin 666 adv.gif
===
Subject: My ex. girl friend in web cam
<!DOCTYPE HTML PUBLIC -//W3C//DTD HTML 4.0 Transitional//EN>
<HTML><HEAD>
<META content=MSHTML 6.00.2800.1276 name=GENERATOR>
<STYLE></STYLE>
</HEAD><FONT face=Arial><FONT size=2>
<BODY>
<DIV>Send email to gzgimsun@163.net or</DIV>
<DIV>&nbsp;</DIV>
Call +86 13802741877 Law Yau.<BR><BR>
<DIV><IMG alt=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
hspace=0
src=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
align=baseline
border=0></DIV></BODY></HTML></FONT></FONT>
===
Subject: My ex. girl friend in web cam
<!DOCTYPE HTML PUBLIC -//W3C//DTD HTML 4.0 Transitional//EN>
<HTML><HEAD>
<META content=MSHTML 6.00.2800.1276 name=GENERATOR>
<STYLE></STYLE>
</HEAD><FONT face=Arial><FONT size=2>
<BODY>
<DIV>Send email to gzgimsun@163.net or</DIV>
<DIV>&nbsp;</DIV>
Call +86 13802741877 Law Yau.<BR><BR>
<DIV><IMG alt=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
hspace=0
src=http://free.eŽle.com.cn/babyromeo/CS MeiMei.jpg
align=baseline
border=0></DIV></BODY></HTML></FONT></FONT>
===
Subject: China girl in Paris
<STYLE></STYLE></HEAD><FONT face=Arial><FONT size=2>
<BODY><DIV>Send email to gzgimsun@163.net or Contact me
+8613802741877
Holland Kin.</DIV><BR><BR>
===
Subject: Re: Feynman in The pleasure of Žnding things out
Received-SPF: none (mailbox1.ucsd.edu: domain of
newsadm@attbi.com does not
designate permitted sender hosts)
http://www.amasci.com/feynman.html
===
Subject: Re: Basic QM Question
> Let¹s say we write down the Schroedinger equation for
hydrogen. We
> then solve it and get among other things the pdf for the
electron¹s
> orbit.
> My question is: why didn¹t I use the pdf of the electron as
a form
> factor in the coulomb interaction. It seems like we start
with a point
> the assumption.
> Is the calculation an apporoximation or is there some
fundamental
> reason? (And can a reason be given without invoking QFT?)
The form factor is _not_ a proability distribution but a
factor in the
effective Schroedinger or Dirac equation. Hence there is no
contradiction.
Arnold Neumaier
===
Subject: vacuum energy anomaly
The energy of the vacuum is calculated at 10^120 J/m^3.
The cutoff energy used to gain this Žgure is 10^19 J.
What cutoff energy is needed to get an energy density
which matches observation (about 10^-10 J / m^3)?
===
Subject: Re: Diffeomorphisms, LQG, and positive energy
> Alas, it is well known in Želd theory (and string theory,
they are
> not different in this respect), that there are no
gravitational
> anomalies in 4D whatsoever, see e.g. Weinberg, Chapter 23.
So if
> such theories are quantized canonically, the diffeomorphism
> generators cannot be unitarily and non-trivially
represented on a
> weakly-continuous Hilbert space! And if these theories
don¹t admit
> a canonical quantization, even in principle, something very
weird
> is going on.
Weird indeed, even if I just understood the sketch of the
argument, I
have a question right from the beginning though.
I understand lowes energy type simply means there is a lowest
energy
in the system? Quick googling doesn¹t lead to any more precise
deŽnitions, could you point me the right way if I¹m far off?
In particular, they notice that one can do LQG quantization
of the
harmonic oscillator, and obtain an energy spectrum which is
not
bounded from below. Needless to say, this is bad news for LQG.
In diffeomorphism invariant context we have no good deŽnition
of
energy to begin with even in classical physics. Is this result
obtained here then truely such a critical problem for LQG?
It¹s not
expected that there is a physical energy observable in QG to
begin
with.
---
frank
===
Subject: Re: quantum theory of gravity
> Why does there seem to be such a bias towards searching for
UniŽcation
> through a quantum theory of gravity when this rules out
half of the
> solution space? Wouldn¹t a curvature theory of quantum
mechanics be
> just as illuminating? What is it that makes searching for a
GTR basis
> for of quantum mechanics any more insurmountable than
Žnding a quantum
> mechanical basis for gravity? Both are equally likely to
exist and
> Žnding either will point to the other.
As others have mentioned there are approaches to modify QM to
accomadate GR, and there are appraoches that modify both.
Personally, I¹m more stimulated by approaches that do
niether. Here is
how it works:
Nature is a subset of the Universe, it is the set of all
phenomena
that we consciouslly observe. The principles of relativity and
uncertainty describe nature, they describe our conscious
experience of
the universe. A bold scientist who wishes to describe nature
could
ignore nature and instead focus on the larger, deeper
Universe. The
Universe is deŽned in such a way that does not include the
principles
of relativity or uncertainty as postulates but instead as
consequences
that are demonstrated by the by-product subset that
represents nature.
In other words, you could unify QM and GR by understanding
that they
are theories of nature, and then create a superset of nature.
Oddly enough the Žrst traces of this type of understanding
were
suggested by Leibniz centuries before both QM and GR.
===
Subject: Re: Where did the main (anti)commutation relation go?
> In the path integral formulation of QFT for bosons,
> the canonical commutations relations are not
> even mentioned. (Ref: Peskin & Schroeder, ch9).
The path integral formulation is a different formulation than
the operator
formulation. Because there are no real operators acting on
the Hilbert
space in this approach, there are also no commutators as you
know them.
The variables that you integrate over are thought of as
purely classical,
commuting (or anticommuting, for Grassmann numbers between
each other)
conŽgurations. The uncertainty principle is režected by the
jitteriness of the typical contributions to the path
integral, and the
closest thing to the nonzero commutator can be derived from
ordering
ambiguities, resulting from the ultraviolet behavior of
correlators.
Your multiply repeated question (of course that the answer to
your
question is identical in QED, lambda.phi^4, as well as for
fermions) can
already be asked in quantum mechanics and has nothing special
to do with
either write the path integral purely in terms of
conŽgurations of x(t) -
and there is no p in this description - or a path integral
involving
both x(t) and p(t), in which you can more transparently see
the nonzero
commutator. Only the Žrst case - the conŽgurations of x(t)
separately -
is naturally generalized in relativistic quantum Želd theory
- and the
question what is the commutator is not really well-posed in
Feynman¹s
approach. The goal of Feynman¹s approach is to calculate the
amplitudes of
the evolution operators between particular initial and Žnal
states.
It is these amplitudes that are equal like those derived from
the operator
formalism - which does not mean that Feynman¹s approach must
copy the
machinery of operators. It does not.
> But L_0 contains phi^dot which doesn¹t commute with phi (at
least,
> that¹s what happens in the canonical formalism).
The path integrals treats phi(x^mu), and consequently also its
derivatives, as classical numbers (integration variables),
and they do
commute with one another. You are not integrating over
operators! The
ordering issues are režected in the ultraviolet behavior of
correlators
(=path integral with insertions).
See e.g. Feynman-Hibbs¹ book about the path integrals
http://www.amazon.com/exec/obidos/tg/detail/-/0070206503/
Best
Lubos
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Re: some questions about gravity
> Two large spherical masses initially at rest, will
accelerate towards
> one another because of gravity.How do the gravitational
waves produced
> by the accelerating masses behave:do they interfere
constructively in
> the space between the masses?
Yes, and also destructively, but only to a very negligible
extent,
as far as the infall itself and the generation and
transmission of the
waves is concerned.
> And does the amplitude of the waves
> increase as the masses get closer together?
Yes.
> As the masses get very
> close they will become non-spherical.How would this affect
the
> gravitational waves between them?
In a very complicated way. Unless the two masses are black
holes or
neutron stars, they collide or get torn up long before there
is any
signiŽcant effect from the gravitational waves.
Even two black holes colliding head on only radiate about one
or at
most a few percent of their rest mass energy in gravitational
waves.
If two blackholes spiral into each other in a nearly circular
orbit,
the percent of energy radiated may get up in the neighborhood
of 30%.
Best,
Jim Graber
===
Subject: Emergence of a 4D World from Causal Quantum Gravity
What do you gravity experts think of:
Emergence of a 4D World from Causal Quantum Gravity
J. Ambj=F8rn, J. Jurkiewicz, and R. Loll
http://prl.aps.org/
===
Subject: Magnetic Monopole
How much disruption or inconvenience would mainline physics
theories
suffer if a magnetic monopole were found. GTR would not be
impacted.
What of the quantum type theories?
Bob Kolker
===
real, and just a calculational device. This has confused me
for two
reasons
indistinguishable, so that if you swap two electrons around
you would
never be able to tell. So if a virtual electron-antielectron
pair is
created, if we could somehow swap the virtual electron for a
real
electron how would we know ? However this
indistinguishability idea
seems (to me at least) to be at variance with the view that
virtual
2. In Stephen Hawking¹s calculation of a black hole¹s
temperature, the
near the event horizon, and one falls in to the black hole,
and the
other is emitted (at least this is how I have seen it
explained). In
exist) somehow become real !
forward a sufŽciently convincing argument to the contrary.
Ian Taylor
===
Subject: Re: nonlinearities in QFT
> I was reading a few more papers on arxiv.org:
> http://www.arxiv.org/abs/quant-ph/0003083
> http://www.arxiv.org/abs/quant-ph/0006079
> In the Žrst paper Johan Hansson proposes that perhaps the
> nonlinearities inherent in the nonabelian parts of the
standard model
> are responsible for the collapse of the wavefunction (which
would
> then, it seems, actually be a deterministic yet nonlinear
and
> therefore unpredictable occurance).
Œ¹The nonabelian vector gauge Želds are governed by a set of
coupled,
second order, nonlinear PDEs on Minkowski spacetime.¹¹
Clearly, this mistakes the classical nonlinear dynamics of
nonabelian
gauge Želds for nonlinear quantum dynamics. But relativistic
QFT does
not give a well-deŽned dynamics at all; all it deŽnes is an
S-matrix.
On the other hand, it is quite possible that a solution of
the unresolved
issues in relativistic QFT are related to the unresolved
issues in
quantum measurement theory.
Arnold Neumaier
===
Subject: top 10 nano products
X-psw: PyModerator 0.3
http://www.justreminding.com/top10nanoproducts.html
===
Subject: Heating stage
X-psw: PyModerator 0.3
Anyone knows where I can Žnd some detailed information about
fabrication
of heating stages for optical, epi, microscopes?
- For oil objectives,
- able to avoid large heat gradients,
- maybe with a žow cell?
Nikodem
===
Subject: Advanced Nanotech Conf: Updated Program - Speakers
X-psw: PyModerator 0.3
1st CONFERENCE ON ADVANCED NANOTECHNOLOGY:
RESEARCH, APPLICATIONS, AND POLICY
Crystal City Marriott Hotel
Washington, DC area
The 1st Conference on Advanced Nanotechnology:
Research, Applications, and Policy is next
month. Please join us as we examine
nanotechnology from three different
perspectives.
Friday is designed for researchers and
technologists, while Saturday and Sunday
will make the applications and policy issues
surrounding nanotechnology understandable to
public interest representatives, investors,
the general public, and those aiming at a
career in the Želd.
CONFERENCE HIGHLIGHTS
Over 30-Speakers, October 22-24 (Friday-Sunday)
Luncheon Address, October 22 (Friday)
Keynote Speaker, October 22 (Friday)
Foresight Feynman Prize Gala Banquet, October 22 (Friday)
Poster Sessions, October 22-24 (Friday-Sunday)
Student Network Event, October 23 (Saturday)
Privacy Debate - October 23 (Saturday)
Special Interest Groups, October 22-24 (Friday-Sunday)
For full schedule click here:
To review Abstracts follow this link:
The Hotel group rate deadline is
reservations now to receive the group rate.
REGISTER NOW:
Foresight Institute offers you several
registration options to the 1st Conference
on Advanced Nanotechnology.
Each day of the conference is dedicated to
in-depth exploration and discussion of a
critical area driving molecular manufacturing:
* Research status on Friday
* Disruptive applications on Saturday
* Policy issues on Sunday
Attendees can customize the conference to
meet their speciŽc interests by using the
one-day, two-day, or three-day option.
To register, go to:
SPONSORS - 1st ADVANCED NANOTECHNOLOGY CONFERENCE
Draper Fisher Jurvetson
http://www.dfj.com/
Howard, Rice, Nemerovski, Canady, Falk and Rabkin
http://www.howardrice.com/
NanoTITAN
http://nanotitan.com/index.htm
SPONSOR - 1st SYMPOSIUM ON MOLECULAR MACHINES SYSTEMS (FRIDAY
RESEARCH)
Sun Microsystems, Inc.
http://www.sun.com/
Foresight Institute
PO Box 61058
Palo Alto, CA 94306 USA
tel +1 650 917 1122
fax +1 650 917 1123
foresight@foresight.org
www.foresight.org
******************************************
Foresight Institute is the leading think tank and
public interest organization focused on
nanotechnology. Formed in 1986 by K. Eric Drexler
and Christine Peterson, Foresight dedicates itself
to providing education, policy development, and
networking to maximize beneŽts and minimize
downsides of molecular manufacturing.
===
Subject: NanoAging.com
X-psw: PyModerator 0.3
NanoAging.com is up again, click www.nanoaging.com
--Jon
===
Subject: Rice Žnds Œon-off switch¹ for buckyball toxicity
X-psw: PyModerator 0.3
Well, Žnally about that controversy:
Researchers at Rice University¹s Center for Biological and
Environmental Nanotechnology (CBEN) have demonstrated a
simple way to
reduce the toxicity of water-soluble buckyballs by a factor
of more
than ten million.
The research will appear in an upcoming issue of the journal
Nano
Letters, published by the American Chemical Society, the
world¹s
largest scientiŽc society. One of the Žrst toxicological
studies of
buckyballs, the research was published online by the journal
on Sept.
11.
Full story at http://www.physorg.com/news1308.html
===
Subject: Nanotechnology applied on aging www.nanoaging.com
X-psw: PyModerator 0.3
Nanotechnology applied on aging www.nanoaging.com
Feel free to join this new nanotechnology project,
--Jonathan
===
Subject: Re: Nanotechnology applied on aging www.nanoaging.com
X-psw: PyModerator 0.3
> Nanotechnology applied on aging www.nanoaging.com
> Feel free to join this new nanotechnology project,
> --Jonathan
the nanotechnology is improving and the mans life span can be
increased to
120.
===
Subject: Administrivia: Welcome to sci.nanotech!
X-psw: PyModerator 0.3
Welcome to sci.nanotech, a moderated group for discussions
related to the
Želd of nanotechnology.
IMPORTANT! Newcomers: BEFORE posting any questions, you
should FIRST read
the material concerning this newsgroup at the web site:
<http://sci.nanotech.dyndns.org/>
This site contains answers to Frequently Asked Questions
(FAQs) as well as
the posting policies. Since this is a moderated newsgroup,
any postings not
conforming to these policies are subject to rejection.
interesting forum for talking about nanotechnology!
===
Subject: C60 fullerene with O-atoms
X-psw: PyModerator 0.3
A Žle has just been posted which shows how twenty
crystal-forming
units (CFUs) of graphite, each consisting of three C-atoms,
can act as
the triangular panels of a regular octahedral assembly. The
Žle also
shows how an O-atom can join with any of the sixty C-atoms of
the
assembly. The Žle may be downloaded at the URL
http://homepage.mac.com/whitby/Quasicrystals/FileSharing171.
html
===
Subject: Re: C60 fullerene with O-atoms
X-psw: PyModerator 0.3
> the triangular panels of a regular octahedral assembly. The
Žle also
The line should read --
> the triangular panels of a regular> ICOSAHEDRAL <assembly.
The Žle also
===
Subject: Icosahedral assembly of graphite CFUs with cleftly
joined
C-strands
X-psw: PyModerator 0.3
A Žle has just been posted which shows how a strand of
C-atoms can
join with a C-atom of one of the twenty graphite CFUs of an
icosahedral assembly. This document shows, by extension, how a
C60-fullerene can join with an atom of a water molecule, a
lipid, a
lone peptide, or a protein. The URL links to the download
page--
http://homepage.mac.com/whitby/Quasicrystals/FileSharing172.
html
===
Subject: SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
My company wants to buy a high resolution SEM. I¹ve looked
briežy
at Zeiss, Hitachi, and JEOL.
I¹ve been told that FE is the way to go but cold FE isn¹t
worth the
trouble.
We will be looking at a wide variety of samples, especially
photoresist on silicon wafers.
I¹ve used a JEOL-35C and a Hitachi 3500H.
I would appreciate any suggestions on manufacturers or models.
===
Subject: Re: SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
>My company wants to buy a high resolution SEM. I¹ve looked
>briežy at Zeiss, Hitachi, and JEOL.
>I¹ve been told that FE is the way to go but cold FE isn¹t
worth
>the trouble.
>We will be looking at a wide variety of samples, especially
>photoresist on silicon wafers.
>I¹ve used a JEOL-35C and a Hitachi 3500H.
>I would appreciate any suggestions on manufacturers or
models.
> If you are looking at diced wafers, that is one factor. If
you
> are looking at whole wafers, that changes things a bit. Are
you
> coating the specimens? What is high resolution for your
work?
> Cold FE will produce high rez images. The issue with them is
> that the tips need žashing once or twice a day. The other
> factor is that they are not really stable for long imaging
times
> like EDS maps or EBSD. Thermal FE systems are very stable.
> Plus, they can produce much higher probe current.
> I use an FEI Sirion SFEG which will do good work looking at
> photoresist on wafers or runners. It has a high magnetic
Želd
> Žnal lens. The Zeiss/LEO Supra 55VP that I have uses an
> electrostatic Žnal lens and has no Želd at all at the pole
> piece. 200KX images at 1KV, 3mm WD and realized rez of
1.7nm.
> In VP mode, it does about 22nm. The Zeiss has all
electronics
> in the column (plinth) unit. FEI has electronics in the
column,
> user table and a separate expansion box. So space could be
an
> issue.
> JEOL makes good SEMs but they seem to be more popular in the
> East than here in the West coast area. So service is an
issue I
> think. FEI has good service all over as far as I know. Zeiss
> has some problems. Mostly understaffed.
> Gary Gaugler, Ph.D.
> Microtechnics, Inc.
> Granite Bay, CA 95746
> 916.791.8191
> gary@microtechnics dot com
This will be used in a research setting so we will be looking
at
samples of all sizes. 4 wafers will be about the largest size.
We must be able to accurately measure features that are 10 -
20 nm
wide and 30 - 40 nm high. The features are made out of
polymers and
can not be coated. Other samples may be coated as necessary.
For this we would ideally like 1 nm resolution but 1.5 - 2 nm
seems
like the best that we could get. I¹m assuming that if we can
get
the resolution we want for a polymer that other sample types
would
be easier.
I think we want to stay away from cold FE for the reasons you
mentioned. I heard a rumor that JEOL will discontinue their
cold
FE SEMs.
Since we want high resolution and magniŽcation at low
accelerating
voltage we will probably not get a VP machine.
How old is your FEI machine?
I know we would be able to get prompt service from JEOL or
Hitachi.
I¹ve never dealt with Zeiss.
The Zeiss sounds like a very nice machine. I have been told
that
they have the best column design. No magnetic Želd could be
useful to look at MEMS devices. Are you happy with this
machine?
Any annoying tendencies? Do you have a service contract?
===
Subject: Re: SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
I use the Hitachi 4800. Its excellent for top down and
cross-section
analysis.
===
Subject: Re: SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
> I use the Hitachi 4800. Its excellent for top down and
> cross-section analysis.
What kind of resolution do you get? On a good day the 3500H I
used
could do, maybe, 10 nm at 5KV. We would really like high mag
at low
accelerating voltages. We want to accurately measure 10 nm -
20 nm
lines.
Any particular problems with your SEM?
===
Subject: Re: SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
SEM is not my forte but (the famous but) the manufacturer
might be less
important than the service. I would ask who in your
neighborhood has the
best service, both price and techs?
Kevin
> My company wants to buy a high resolution SEM. I¹ve looked
briežy
> at Zeiss, Hitachi, and JEOL.
> I¹ve been told that FE is the way to go but cold FE isn¹t
worth the
> trouble.
> We will be looking at a wide variety of samples, especially
> photoresist on silicon wafers.
> I¹ve used a JEOL-35C and a Hitachi 3500H.
> I would appreciate any suggestions on manufacturers or
models.
===
Subject: Major breakthrough in nanotubes?
X-psw: PyModerator 0.3
Ultralong single-wall carbon nanotubes.
http://www.nature.com/cgi-taf/DynaPage.taf?Žle=/nmat/journal/
vaop/ncurrent/
abs/nmat1216.html&dynoptions=doi1096137264
Extra-long carbon nanotubes set new record
A longer strand of tiny tough stuff.
The researchers have produced 4cm length single walled
nanotubes.
They claim the method can be scaled to produce arbitrarily
long
nanotubes.
Bob Clark
===
Subject: CFV: sci.techniques.microscopy.scanning-probe
Archive-Name: sci.techniques.microscopy.scanning-probe
iD8DBQFBWtXiXMotZRinPKkRAmGFAKCOMN9Wh97bqr54EbkZ8SajupLzoQCdGh
Jm
fD5+dppW1G+4gFuDR5VvnNQ=
=625A
FIRST CALL FOR VOTES (of 2)
unmoderated group sci.techniques.microscopy.scanning-probe
Newsgroups line:
sci.techniques.microscopy.scanning-probe Scanning probe
microscopy.
This vote is being conducted by a neutral third party.
Questions about
the proposed group should be directed to the proponent.
Proponent: Jim Logajan <JamesL@Lugoj.com>
Proponent: Thom Borton <borton@phys.ethz.ch>
Proponent: Gordon Vrdoljak <gvrdolja@nature.berkeley.edu>
Votetaker: Bill Aten <bill@netagw.com>
RATIONALE: sci.techniques.microscopy.scanning-probe
The proposed newsgroup should be created because it will
provide an
open forum for the discussion of techniques and current
research of
scanning probe microscopy. The newsgroup
sci.techniques.microscopy
has become a de facto forum for discussion of optical
microscopy,
which has little in common with scanning probe microscopy.
Currently,
a private mailing list of one SPM vendor has a good amount of
activity, with an active membership of a couple thousand
users and an
average of several daily postings. And the Želd continues to
grow,
both in users and vendors.
The group will provide the SPM community a forum that is more
publicly
accessible and easier to read (e.g. direct support for
threads) than
the privately subscribed mailing list. The advent of feature
rich web
searchable archives by entities such as Google Groups is
another
advantage of using Usenet over that of a private list.
Usenet¹s
inherently distributed nature makes multiple archives both
possible
and likely, while the same is not so easily done with a
private
mailing list.
The current mailing list is run by the leading microscope
manufacturer
and has provided the scanning probe community a great public
service,
for which they must be commended. Postings on issues about
systems
from other companies or from the large community of
researchers who
built their own microscopes do come up occasionally, yet many
more in
the community have not thought of subscribing to the mailing
list -
either because they are unaware of it, believe it focuses
only on that
manufacturer¹s equipment, or disagree with its list of banned
topics
(such as comparisons or reviews of competitive equipment or
relevant
job postings from commercial entities). An unmoderated
newsgroup
would attract a much wider audience to share information and
would
complement the existing mailing list.
The issue of spam is a concern of many. The amount of spam
that such
a group is likely to receive can be estimated by reviewing
the Google
Groups archive of the nearest relevant newsgroup,
sci.techniques.microscopy newsgroup:
~9 spam messages out of ~412 messages posted. (N.B. Google
even
archives spam.) The level at which spam becomes a signiŽcant
irritation is a subjective issue, but relative to regular
e-mail, a
~2% rate may be considered quite low.
CHARTER: sci.techniques.microscopy.scanning-probe
This group is an open forum for the discussion of techniques,
theory,
instrumentation, and research in the use of scanning probe
microscopes. Such technologies include any form of microscopy
that
involves the scanning of a probe close to a surface. This
includes,
but is not limited to: atomic force microscopy (AFM), scanning
tunneling microscopy (STM), magnetic force microscopy (MFM),
chemical
force microscopy (CFM), lateral force microscopy (LFM), and
near Želd
scanning optical microscopy (NSOM or SNOM). Postings
advertising job
openings directly from the hiring Žrms (i.e. not recruiters)
that
require expertise in SPM techniques, theory, instrumentation,
and
research would also be appropriate, provided they are not
repeated.
Binaries and postings entirely unrelated to any of the above
would not
be appropriate and posters are asked to post them to more
appropriate
groups.
END CHARTER.
HOW TO VOTE:
Extract the ballot from the CFV by deleting everything before
and after
the BEGINNING OF BALLOT and END OF BALLOT lines. Don¹t worry
about
the spacing of the columns or any quote characters (>) that
your
reply inserts.
PLEASE, do not send the entire CFV back to me as this mail is
archived.
Mark the ballot and then MAIL it to:
<microscopy-vote@netagw.com>
(or established Usenet handle) and indicate your desired vote
in the
appropriate locations inside the ballot.
Examples of how to properly indicate your vote:
[ YES ] example.yes.vote
[ NO ] example.no.vote
[ ABSTAIN ] example.abstention
[ CANCEL ] example.cancellation
DO NOT modify, alter or delete any information in this ballot!
If you do, the voting software will probably reject your
ballot.
If you do not receive an acknowledgment of your vote within
three
days, contact the votetaker about the problem. You are
responsible
for reading your ack and making sure your vote is registered
correctly.
|------------------------------------------------------------
----------
| OfŽcial CFV Name: sci.techniques.microscopy.scanning-probe
| Usenet Voting Ballot [STMSP-81-1] (Do not remove this line!)
|------------------------------------------------------------
----------
| Please provide your real name, or your vote may be rejected.
| Established Usenet handles are also acceptable. Place ONLY
your name
| (ie. do NOT include your e-mail address or any other
information;
| ONLY your name) directly after the colon in Voter name: on
the
| following line.
|------------------------------------------------------------
----------
| Voter name:
|------------------------------------------------------------
----------
| Insert YES, NO, ABSTAIN, or CANCEL inside the brackets for
each
| newsgroup listed below (do not delete the newsgroup name):
|
| Your Vote Newsgroup
| --------- ---------
| [ ] sci.techniques.microscopy.scanning-probe
|
|------------------------------------------------------------
----------
IMPORTANT VOTING PROCEDURE NOTES:
Standard Guidelines for voting apply. Only one vote per
person, no
more than one vote per account. Votes must be mailed directly
from
the voter to the votetaker. Anonymous, forwarded, or proxy
votes
are not valid. Votes mailed by WWW/HTML/CGI forms are
considered
to be anonymous votes.
Vote counting is automated. Failure to follow these
directions may
mean that your vote does not get counted. If you do not
receive an
acknowledgment of your vote within three days, contact the
votetaker
about the problem. It¹s your responsibility to make sure your
vote
is registered correctly. Duplicate votes are resolved in
favor of
the most recent valid vote. Names, addresses, and votes of
all voters
will be published in the Žnal voting results post.
DO NOT redistribute this CFV in any manner whatsoever. The
purpose of
a Usenet vote is to determine the genuine interest of persons
who would
read a proposed newsgroup. Soliciting votes from
disinterested parties
defeats this purpose. Only the votetaker, the
news.announce.newgroups
moderator, and the proponent (if speciŽcally authorized by
the votetaker)
are permitted to distribute copies of this CFV.
Distribution of pre-marked or otherwise modiŽed copies of
this CFV is
generally considered voting fraud and should be reported
immediately to
the votetaker or the UVV <contact@uvv.org>. In cases where
voting fraud
is determined to have occurred, it is standard operating
procedure to
delete ALL votes submitted by the violator. When in doubt,
ask the
votetaker.
DISTRIBUTION:
The only ofŽcial sources for copies of this CFV are the
locations listed
below, the UVV web site at http://www.uvv.org/, and the
votetaker¹s e-mail
CFV server which can be reached at
<microscopy-cfv-request@netagw.com>.
This CFV has been posted to the following newsgroups:
news.announce.newgroups
news.groups
sci.nanotech
sci.physics
sci.techniques.microscopy
Pointers directing readers to this CFV will be posted in
these newsgroups:
sci.engr.micromachining
sci.materials
sci.physics.research
and to the following mailing list:
Mailing list name: DI SPM List
Submission address: spm@di.com
Request address: http://spm.di.com/listinfo.html
===
Subject: Re:[Sci.nanotech] SEM question/advice, best FE SEM?
X-psw: PyModerator 0.3
We have had a lot of problems with imaging isolated metal
features on
insulating samples (glass). Image can drift while viewing or
measuring
linewidth.
The energy is already such that charging is minimized but
this is
different for the two different materials, so there can still
be net
charging of the Želd. I am not sure if any manufacturer has a
magic
bullet to address this.
I did hear about Environmental Secondary Electron Microscopes
(ESEMs)
http://www.itg.uiuc.edu/ms/equipment/microscopes/esem/ but I
am not sure
if they offer the precision or resolution you or I need. FEI
is cited as
a manufacturer at the given link.
On another thread (sci.materials), I received several
recommendations to
coat with a discharging layer, but I¹d rather make sure this
can be
removed without damaging the sample in any way.
Fred
-----Original Message-----
[mailto:sci.nanotech-bounces@nano-tek.org] On Behalf Of Dev
Null
===
Subject: [Sci.nanotech] SEM question/advice, best FE SEM?
My company wants to buy a high resolution SEM. I¹ve looked
briežy
at Zeiss, Hitachi, and JEOL.
I¹ve been told that FE is the way to go but cold FE isn¹t
worth the
trouble.
We will be looking at a wide variety of samples, especially
photoresist on silicon wafers.
I¹ve used a JEOL-35C and a Hitachi 3500H.
I would appreciate any suggestions on manufacturers or models.
_______________________________________________
sci.nanotech mailing list
sci.nanotech@nano-tek.org
http://venusia.golgothe.net/mailman/listinfo/sci.nanotech
===
Subject: Re: Landscape averages - paper of the day -
Kumar+Wells
It¹s a nice paper as it makes a deŽnite claim: the
distribution of
the rank N of the gauge group in string compactiŽcations goes
as
exp -N/N_{avg} for some relatively small N_{avg}.
While I think the argument Kumar and Wells give is sensible
and
interesting, it depends on unjustiŽed assumptions, which
makes the
claim rather preliminary (as admittedly are all claims in
this area at
this point). Of course one of these is the idea that the
number of D3
branes dominates the rank of the gauge group or is
distributed the
same way, as there are many other types of D-branes with
different
matter content etc.
However the main point left out is that theories with gauge
sectors
tend to have a larger multiplicity of vacua, because their
matter must
be stabilized and this will lead to many vacua. In the case
of D3¹s
this at least includes their position moduli on the CY, which
by
arguments given in my 0303194, for N D3¹s would be expected
to have of
order chi(Sym_N M), the Euler character of the N-fold
symmetric
product of the CY M. For most CY¹s this is a pretty large
factor
which dominates at low N and pushes the peak of the
distribution up,
though the large N tail would still be exponential.
I am somewhat suspicious of the large N behavior being
exponential, on
empirical grounds: there are known to be F theory
compactiŽcations to
four dimensions with N=1 supersymmetry with gauge group ranks
of
order 100000 (Candelas et al), which is pretty unlikely to
come out of
the distribution exp -N/N_{avg} with small N_{avg}. I suspect
the
number of vacua is more likely to fall off as a power of N,
but do not
yet have a good argument for this.
Finally, I would like to say that the idea of a landscape
average is
NOT mine and does not describe my work. First, as a minor
point, I
don¹t usually use the term landscape -- but this is just my
own
taste, landscape is a good term which just emphasizes other
aspects of
the problem, such as the structure of the potential and
barriers
between vacua, than the ones I have been working on.
More importantly, as explained in 0303194, my recent 0409207,
etc., I
think it is meaningless to average over different vacua,
because we
only observe one vacuum. Rather, the goal of my own work, and
what I
advocate doing, is to characterize the distribution of vacua
well
enough to estimate the number N_SM of different vacua which
satisfy
the many existing observational constraints (standard model,
cosmological, etc.) as well as possible future constraints
(this might
lead to predictions as discussed in 0409207). Based on this
information, we can decide whether we should continue the
search for
the right vacuum directly (appropriate if N_SM <= a few),
look for
additional principles to cut down the number (if N_SM is
large), or
give up and start making anthropic arguments or whatever (if
N_SM is
ridiculously large). These works describe many other ways to
use this
information, for example to know which properties are common
in
string/M theory (so less interesting) or rare (so more
interesting and
more selective).
So for me, a quantity like the average rank of the gauge
group, while
well deŽned, is not directly physically meaningful, and not
to be
considered as a preferred value (just as the actual height of
any
single human is unlikely to be equal to the average height of
a
human). It is useful, but just as a way of characterizing the
distribution (as in the exp -N/N_{avg} above).
===
Subject: Stringy naturalness
provoking recent review
http://www.arxiv.org/abs/hep-th/0409207
Well, Peter Woit made some comments about the situation on
his blog
http://www.math.columbia.edu/~woit/blog/
on September 20th - his summary is that you say that string
theory
predicts that we can never see any physics related it. It
would be too
difŽcult for me to pretend that I disagree with these Woit¹s
remarks.
Do I understand well that all these predictions of yours
about the
nonexistence of low energy SUSY and large dimensions
critically rely on
your deŽnition of stringy naturalness? You describe your
notion of
stringy naturalness very explicitly:
(**) An effective Želd theory (or speciŽc coupling or
observable)
T1 is more natural in string theory than T2, if the number
of phenomenologically acceptable vacua leading to T1 is larger
than the number leading to T2.
I could not disagree more. This very deŽnition of naturalness
already
seems to contain - assume, in fact - Woit¹s result that the
most typical
prediction of this approach to string theory will be that
there are no
predictions. According to (**), the more ambiguous and
unpredictive
something is, the better.
Also, I don¹t think that this counting the more vacua, the
more natural
generalizes the notion of naturalness from physics before
string theory
in any natural way. I would say that naturalness means - and
always meant
- that the parameters that naturally appear in the
description of physics
should be of order one. There are inŽnitely many more numbers
(even among
integers!) :-) that are *not* of order one (for example
1235235236236236),
but this makes them *less* natural, not more, does not it?
If the notion of stringy naturalness were deŽned using the
number of
vacua, I would probably choose a deŽnition which seems to be
nearly the
opposite of (**), namely
(##) An effective Želd theory or physical mechanism - or a
value
of a coupling or another parameter - is natural from the
stringy viewpoint if it can be expected to be reproduced
in stringy backgrounds whose adjustable discrete parameters
are of order one, i.e. backgrounds that are simple.
A more rigorous deŽnition what is simple and what exactly
should be of
order one requires some deeper knowledge of physics than what
we have, but
the rough philosophy difference seems clear, I think.
Note that this deŽnition more or less implies that the number
of the
discrete natural vacua with (approximately) the desired
properties will
also be of order one, while your natural vacua are by
deŽnition
members
of huge families (unnatural families, in my language).
I think that it is (##), not (**), that naturally generalizes
the previous
notions of naturalness. Naturalness means that the properly
deŽned
parameters are of order one - not too small and not too
large. The only
open question is what it means a properly deŽned/parameterized
parameter i.e. what is the measure, and deeper mechanisms
such as
those
in string theory are here to answer the question.
Because of experimental observations, we simply know that
some ratios in
Nature - such as m_{planck} / m_{electron} - are extremely
large. These
hierarchies of many types are simply a property of Nature and
we can¹t do
anything about them - except for trying to explain them (Žrst
qualitatively, and then perhaps quantitatively). The Žrst
obvious comment
is that these large values seem *unnatural*. However, many
such large
ratios are only unnatural until we learn and understand the
physical
effects that are underlying them. For example, it is not so
shocking that
m_{planck} / m_{QCD} is so large - once we realize that
g_{strong} at the
scale m_{planck} is a mildly small number of order one, and
because
g_{strong} only runs logarithmically, it is guaranteed to
reach one at a
much smaller energy scale.
Similarly, the large total mass of visible non-relativistic
matter
(expressed in Planck units) in the Universe today (it has not
changed too
much for billions of years, I think) can be explained by a
reasonable
number of e-foldings of inžation (which is able to produce
mass from
nothing).
This is what I personally call a natural explanation of the
large ratio
m_{planck} / m_{QCD}, or a natural explanation of the large
mass of the
Universe - and it is the kind of insights that we should be
trying to
Žnd. The role of string theory is to provide us with more
reliable tools
and mechanisms that can do this job. Do you think that you
would agree
with this statement?
On the other hand, an explanation based on choosing some
things very small
or very large is unnatural, I think. An explanation based on
a multiverse
- or the conglomerate of all vacua in string theory that we
can imagine -
where all parameters can be very small or very large simply
because there
is a large number of such choices - it is a very unnatural
(and
unsatisfying) explanation.
Moreover, we clearly know examples in which we must just Žnd
a scientiŽc
explanation why something is small - the QCD theta-angle
(strong CP
problem) could probably be of order one without spoiling life.
Nevertheless, it is very tiny for no good known (so far)
reason, as we
were emphasized yesterday on a pheno talk by John Donoghue
here.
I would only claim that someone has understood why theta is
small in
string theory if she had a simple realistic model with a
calculation - at
least approximate one - that implies a small value of theta -
or a class
of models where the property holds universally. Finding
10^200 convoluted
žux vacua is just not enough.
This debate may be philosophical today, but I believe that it
will become
very scientiŽc sometime in the future when people actually
try to
understand some cosmological (or other) vacuum selection
mechanisms
because whatever the mechanism will be, it will be favoring
the choices
where the natural parameters are of order one. This means, I
believe,
that such a cosmological mechanism will produce vacua of the
type (##)
rather than the generic convoluted vacua of the type (**).
A toy model: let¹s imagine that the number of Calabi-Yau
topologies is
inŽnite, and chi goes to inŽnity, too. I think it is obvious
that a
cosmological creation will tend to produce Calabi-Yaus with
reasonable
chi¹s of order one, instead of some virtually inŽnite numbers
- simply
because it is also unnatural to create many handles of a
Calabi-Yau. I
think that the reason why it¹s unnatural is the same like the
reason why
the evolution theory is a more natural explanation than the
Creator who
created each species separately ad hoc (the analogy is simply
1 species =
1 handle).
Moreover, as the example above already indicates, it is
conceivable that
if one looks carefully enough, she can discover a discretely
inŽnite
total number of vacua in string theory, in which case the
criterion (**)
breaks completely. On the other hand, there is nothing wrong
with string
theory if it predicts a discrete inŽnite number of vacuum
states (the
harmonic oscillator has an inŽnite number of states, too).
Any reasonable
physical mechanism that actually assigns weights or
probabilities
to
the vacua will not care whether the number of vacua is 10^300
or
discretely inŽnite, which means that according to everything
I can
imagine, any reasoning that leads to very different results
for these two
choices (10^300 vs. inŽnity) must be incorrect - which also
means that
(**) is incorrect. Don¹t you think that it should be
legitimate to
approximate 10^{300} by inŽnity? We can certainly do it for a
harmonic
oscillator without getting too bad answers.
The number of vacua may be large (or discretely inŽnite), but
they always
have some organization, hierarchy, and therefore include some
simple
vacua (analogy of the ground state of the harmonic oscillator
and a few
excited states) where the discrete parameters are of order
one - whatever
it exactly means - and the rest of the tower which are
unnatural
states.
What we should be interested in, I think, are mechanisms that
illuminate
hidden physics behind various numbers, and allows us to
reparameterize
these (large or small) numbers as functions of natural
numbers of order
one. Of course, this includes various mechanisms to generate
numbers in
the exponential form. Inžation and the RG running of
g_{strong} are
examples.
As John Donoghue has emphasized (also in his yesterday¹s talk
at Harvard),
the scale-invariant form of fermion masses (i.e. the fact
that they are
mostly uniform on the logarithmic scale) has a nice
explanation in
intersecting brane models because the Yukawa couplings come
from disks -
and contain the exp(-A.tension) suppression. Assuming a
uniform
distribution of the areas A (of the triangles - disks -
stretched between
the three intersection points), we naturally obtain the
qualitatively
desired spectrum of the fermion masses.
Even if the number of stable (and so on) stringy vacua
describing these
models with intersecting branes turns out to be of order one,
they will
still be natural, won¹t they? You can Žnd some 10^200 of
other vacua
based on complicated structures of large žuxes, among 10^300
of žux
vacua in general, and it seems that according to your (**)
rule, they will
be 10^200 times more interesting for you than the single
intersecting
braneworld. Well, for me they will be much less interesting -
even though,
of course, they have a higher probability that they happen to
describe the
observations accurately enough.
If one imagines that the single vacuum with intersecting
branes and one
of those 10^200 žux vacua will happen to agree with the
experiments with
the desired accuracy, no doubt, I will prefer the single
intersecting
braneworld - roughly with 10^{200} times bigger happiness
than the žux
vacuum. It¹s simply because this theory has a much smaller
input and is
more natural.
There are other reasons why I think that (**) is obviously
incorrect. Even
if we imagine that the number of vacua is Žnite and
exponentially large,
there is a subtlety. It is almost guaranteed that the
exponents of
different types of vacua will be very different. There can be
10^{300}
type IIB žux vacua, but only 10^{280} vacua of M-theory on G2
manifolds
with žuxes. Does it mean that the IIB vacua are 10^{20} times
more
reasonable choice predicted by string theory? I hope not. It
sounds
completely irrational to me.
Moreover, if the philosophy (**) were taken seriously, to
more general
theories, the most natural theories according to this
criterion would be
non-renormalizable theories because the number of the
corresponding vacua
is inŽnity^inŽnity - one can choose inŽnitely many numbers to
be
anything. These things are just the opposite of what I
imagine to be
natural.
Lubos
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Re: Stringy naturalness
has given real thought to the subject, as is evident in your
paper
0007206.
Your message deserves a longer reply than I have time for
right now,
but let me encourage anyone reading this to look at 0409207
and my
other papers, especially the Žrst two and last sections of
0303194,
for a real explanation of my point of view. But here is a
brief
response to your comments.
First, it is very easy to get hung up in this context on
deŽnitions,
philosophical discussions of what it means to explain
something,
etc. The best way to avoid this is to try to work towards some
objective claim. I have been trying to see if string theory
can be
falsiŽed, in the sense that we could show that some
phenomenon which
might be observed could NOT be reproduced from string theory.
Perhaps
the best candidate for this I know of is time variation
of the Žne structure constant, along lines argued in my
hep-ph/0112059 with Banks and Dine. But it is interesting to
consider
other phenomena, even the standard predictions of low energy
supersymmetry, in this light.
There are various motivations for the deŽnition (**) of
stringy
naturalness, as I explain in 0409207 and elsewhere. The main
reason
for the name is just that it substitutes for and in some
cases gives
different predictions from the traditional deŽnitions of
naturalness.
Another, as I discuss further below, is that it is natural
information about the set of possibilities which can come out
of
string theory, which is an important input into almost any
candidate
vacuum selection principle.
But perhaps the strongest motivation for the deŽnition (**),
as I
explain in 0409207 and elsewhere, is that under certain
assumptions --
mostly, that the number of vacua that we believe are
candidates is in
this 10^100-10^300 range, (**) could lead to believable
arguments that
certain possible physics could NOT be obtained from string/M
theory,
because there are just not enough vacua of that type to tune
the
cosmological constant and get the other parameters right.
I believe that to falsify string theory, one really needs to
argue
that there are NO consistent vacua (coming out of consistent
cosmologies) in the class which reproduces the (current or
hypothetical future) observations. It does not matter whether
the
vacua which do it are complicated or whether we dislike them
for
some other subjective reason. Such falsiŽability was expected
in
previous discussions in which people assumed the existence of
millions
or billions of vacua. A major point of my work is that even
numbers
which seem large, like 10^300, are not necessarily too large
from this
point of view.
The reason 10^300 should not be approximated by inŽnity, while
perhaps 10^1000 could be, is just the amount of data at hand
and the
structure of the problem. As discussed in 0303194, we measure
many
parameters of the SM to some precision, and the cosmological
constant
to fantastic accuracy, and it is the problem of matching this
data
which leads to numbers like 10^240.
At present it is not at all clear what the actual number and
distribution of vacua will turn out to be. Indeed the simplest
conjecture (which I raised in 2001 at JHS60) is that the
number is
inŽnite -- why not. I worked for over a year around 2002
looking for
evidence for inŽnite series of vacua which
might roughly match observations (inŽnite series of CY¹s, of
vector
bundles, of brane conŽgurations etc.) and my tentative
conclusion is
that there are not; there are many inŽnite series (arbitrary
žux in
AdS_5 times S^5 being the simplest illustration) which
however do not
match observation because they have towers of light states
coming
down. An inŽnite series of CY_3¹s might not have this
property, but
the Žnitude of CY_3¹s is a famous conjecture at this point --
this is not to say we know it is true, just that many people
have
thought about it and it is consistent with everything else we
know.
Anyways, more people should be working on trying to Žnd
inŽnite
series of potentially realistic vacua.
Alternatively, it might turn out in the end that the number
is more
like 10^1000. Suppose we prove to our own satisfaction that
there are
10^1000 relevant vacua, which are uniformly enough
distributed that
string theory can reproduce a huge variety of extensions of
the
Standard Model. Now I would consider this a huge victory for
string
theorists, in that we answered a primary question, even if
from some
point of view the answer was negative. We would have a theory
which
could Žt the data, and might lead to interesting new
predictions in
yet unrealized situations.
But one could also go on, and try to propose a principle to
narrow
down the class of vacua, call it principle X, and regain
predictivity.
One could go on to propose arguments justifying it, say that
this
class of vacua comes out of the preferred initial conditions.
But
this is not absolutely necessary -- if a principle cuts down
the
numbers of vacua sufŽciently, one could assume it and try to
make
predictions along the lines I am discussing, and the
principle might
justify itself by its predictions. What is necessary is that
the
principle be precise and pick out a precise class of vacua.
If you
think about this, since the principle will pick a subclass
out of the
preexisting set of possible vacua, using it will still
require the
distribution information which we are studying now. Anyways,
I think
it is interesting to formulate such candidate vacuum selection
principles.
Now, predictions under assumptions such as principle X, cannot
literally falsify the theory, they can only falsify the
combination of
theory + assumptions. Suppose no vacuum satisfying X
reproduces the
observations, while some other vacuum Y not satisfying X, say
it
requires special tuning of the initial conditions, has
parameters
which are not of order 1, etc., actually does. Will you go on
to tell
me that string theory is wrong, that vacuum Y is no good? You
better
have a pretty convincing principle, more so than your (##) I
think.
I think it would be valuable for you to propose any precise
version of
your (##). Whether (##) might also deserve to be called
naturalness
I think depends on what assumptions it is believed to follow
from
(note that there are many variations on the traditional
deŽnition of
naturalness as well, with different names). But it is not
worth
discussing without a precise deŽnition. Is compactiŽcation on
a CY
with hundreds of cycles simpler or more complicated than one
with
a few cycles? Why? As for žuxes, the explicit discrete
parameters
depend on a choice of basis, ambiguous up to Sp(b_3,Z)
transformations. How do I decide if they are order one? And so
on...
Please think about this as while I agree with some of your
comments,
others seem basically wrong to me. For example, the comment
early on
that According to (**), the more ambiguous and unpredictive
something
is, the better. This is totally backwards as the most
interesting
case is of course when the distribution of some observable is
highly
peaked. So, if it were to turn out that the distribution of
the rank
N of the gauge group among vacua was highly peaked at 4, that
would be
quite interesting, and many would consider it a candidate
explanation
for the observed rank of the Standard Model gauge group.
According to
(**), the property N=4 would be highly natural. What does
(##) say
about it?
Best, Mike
===
Subject: Re: Helling & Policastro on GNS quantization of
string
> Then I would like to remark that a subtle but maybe crucial
issue should
not
> be overlooked: The diffeomorphisms discussed by Thiemann
and by
> Helling&Policastro are not the spatial diffeomorphisms which
> reparameterize the spatial slices of the string. As such
they cannot be
> completely compared to the spatial diffeo constraints as
they appear in
the
> ADM constraints of (2 and higher dimensional) gravity.
Correct. Although we start with a canonical 1+1 split, we end
up
discussing the left and right chiral halfs j^pm separately.
So the
Virasoro that we discuss is the chiral symmetry algebra (the
total
conformal symmetry being Vir_left + Vir_right).
> Finally I have a technical question to Robert and Giuseppe
Policastro
> concerning the discussion on pp10-11 of their paper. Maybe
I am mixed up,
> but it seems to me that there at some point commuting and
anti-commuting
> properties need to be exchanged.
Right again. In the text, exchange commuting and
anti-commuting once
and everything should be Žne. All formulas as far as I can
see are
correct.
Robert
--
.
oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oOo.oO
o.oOo.oOo.oOo
.oO
Robert C. Helling Department of Applied Mathematics and
Theoretical
Physics
University of Cambridge
print Just another Phone: +44/1223/766870
stupid .sign; http://www.aei-potsdam.mpg.de/~helling
===
Subject: Re: Helling & Policastro on GNS quantization of
string
Robert C. Helling <helling@ariel.physik.hu-berlin.de> schrieb
im
> Then I would like to remark that a subtle but maybe crucial
issue
should
not
> be overlooked: The diffeomorphisms discussed by Thiemann
and by
> Helling&Policastro are not the spatial diffeomorphisms which
> reparameterize the spatial slices of the string. As such
they cannot be
> completely compared to the spatial diffeo constraints as
they appear in
the
> ADM constraints of (2 and higher dimensional) gravity.
> Correct. Although we start with a canonical 1+1 split, we
end up
> discussing the left and right chiral halfs j^pm separately.
So the
> Virasoro that we discuss is the chiral symmetry algebra
(the total
> conformal symmetry being Vir_left + Vir_right).
Yes. Nothing wrong with that. I just pointed it out because
the whole
discussion is latently about how to quantize gravity and I
believe it is
important to note when we are talking about spatial
diffeomorphisms and
when
about something that just looks like these.
> Finally I have a technical question to Robert and Giuseppe
Policastro
> concerning the discussion on pp10-11 of their paper. Maybe
I am mixed
up,
> but it seems to me that there at some point commuting and
anti-commuting
> properties need to be exchanged.
> Right again. In the text, exchange commuting and
anti-commuting once
> and everything should be Žne. All formulas as far as I can
see are
correct.
Yes, sorry, I did not mean to imply that anything is wrong
with your
computations. I was just checking if I correctly followed
your derivations.
===
Subject: Re: Quantization without quantization
> Quantization without quantization - prejudices and reality
Let me Žrst state that I agree fully with almost all that you
say.
Not unexpectedly, the only one point which I disagree upon is
the
discussion on gauge anomalies, and even there I only disagree
partially. What you say on this issue makes sense and is the
standard lore, but it needs elaboration.
> Reality IVa: Chiral gauge theories and similar theories in
2k dimensions
> typically lead to gauge anomalies. Gauge anomalies imply
that the theory
> is no longer consistent because the unphysical (and
negative-norm)
> polarizations of the gauge bosons (or graviton) no longer
decouple. The
> structure of anomalies can be calculated if one tries to
regularize
> certain UV divergences, but the result is purely režected
by the low
> energy (IR) spectrum of the theory. There is no way to
avoid the
> conclusion about gauge anomalies except for cancelling them.
> Anomalies in global symmetries do not imply an
inconsistency, but they
> drastically inžuence the physics of a given theory.
> Central charge (or Weyl anomaly) is a speciŽc example of an
anomalous
> term that can be calculated in many ways, and there is no
consistent way
> to avoid its nonzero value.
We should Žrst deŽne what we mean by a gauge theory. Since not
all quantum theories have well-deŽned classical counterparts,
we
need a deŽnition which is intrinsically quantum. I propose to
deŽne a gauge symmetry as a symmetry with a well-deŽned,
nilpotent BRST operator. In that case the symmetry is a
redundancy
of the description, because we can deŽne the physical Hilbert
space as the space of BRST cohomology classes.
With this deŽnition, it is tautologically true that no
consistent
gauge anomalies exist. Not because an anomaly would
necessarily
be inconsistent, but because it would ruin nilpotency, making
the
symmetry into a global symmetry (global is a terribly
confusing
word in this context, btw. I would prefer the word non-gauge).
There is nothing intrinsically wrong with anomalous global
symmetries whose non-anomalous part is isomorphic to a gauge
symmetry. The canonical example is the minimal models in CFT
with
central charge 1/2 <= c <= 1. They are physically consistent
in the strong sense that they are realized (and measured!) in
experimentally accessible systems. And still the anomaly-free
part
of the symmetry algebra is isomorphic to the Weyl gauge
symmetry of
string theory.
If we could take the classical limit of such a system, it
would seem
to have a gauge symmetry. Namely, the anomaly vanishes in the
classical limit, and we can write down a classical BRST
operator
which is nilpotent, and the symmetry is gauge on the classical
level. There is no classical way to distinguish between such a
fake gauge symmetry and a genuine gauge symmetry which
extends to
the quantum level. The quantum world is what it is, and
classical
intuition can often go wrong.
Unfortunately, we cannot check this argument for the minimal
models,
because they don¹t seem to have a good classical limit. Some
aspects
can be captured by Landau-Ginzburg models, but others are
totally
opaque in the LG picture, like the supersymmetry of the c =
7/10
model.
Thus some anomalous gauge symmetries (= anomalous global
symmetries
whose non-anomalous part is isomorphic to a gauge symmetry)
may be
consistent, but all are not. It must be realized that gauge
symmetries have two qualitatively different types of
anomalies:
1. Anomalies seen in Želd theory, related to the existence of
chiral fermions. This class include the ABJ anomalies in the
standard model and the Green-Schwartz mechanism. There are
two good
reasons to expect that such anomalies are inconsistent: Nature
avoids them in the standard model, and the corresponding
algebra
does not seem to have any good representations.
2. Anomalies like the Virasoro and afŽne Kac-Moody algebra,
and
their higher-dimensional analogues. These algebras have
interesting
unitary representations, but cannot be seen in Želd theory
because
they involve the observer¹s trajectory. There is no reason to
expect such anomalies to be inconsistent, especially since
they do
arise in condensed matter models like the 2D Ising model.
The different extensions can be illustrated for the current
algebra
on the 3D torus. Use a Fourier basis with momenta m = (m_i)
in Z^3,
structure constants f^abc, second Casimir delta^ab and third
Casimir
d^abc. The Mickelsson-Faddeev algebra describes the ABJ
anomaly:
[J^a(m), J^b(n)] = f^abc J^c(m+n)
+ d^abc epsilon^ijk m_i n_j A^c_k(m+n),
[J^a(m), A^b_k(n)] = f^abc A^c_k(m+n) + delta^ab m_k
delta(m+n),
[A^a_i(m), A^b_j(n)] = 0.
A^a_i(m) are the Fourier components of the gauge connection.
The central extension (which commutes with gauge
transformations
but not with diffeomorphisms):
[J^a(m), J^b(n)] = f^abc J^c(m+n) + delta^ab m_i S^i(m+n),
[J^a(m), S^i(n)] = [S^i(m), S^j(n)] = 0,
m_i S^i(m) = 0.
These two extensions of the current algebra in 3D have thus
very
different properties, and to conclude that inconsistincy of
the
former implies inconsistency of the latter is simply wrong.
Finally, we must deŽne exactly what we mean by consistency.
At the
most basic level, a quantum theory is deŽned by a Hilbert
space
and a unitary time evolution. If the theory has some
symmetries,
they must be realized as unitary operators acting on this
Hilbert
space as well. If time translation is included among the
symmetries,
which is the case for the Poincare algebra (and more subtly
for
diffeomorphisms), requiring a unitary representation of the
symmetry algebra seems to be enough for consistency.
covariant quantum theories (GCQT) and unitary representations
of the
diffeomorphism group on a conventional Hilbert space. Namely,
if we
have a GCQT, its Hilbert space carries a unitary rep of the
diffeo
group. And if we have a unitary rep of the diffeo group, the
Hilbert
space on which it acts can be interpreted as the Hilbert
space of
some GCQT. Since all unitary quantum irreps of the diffeo
group are
anomalous, apart from the trivial one, all interesting GCQTs
carry
anomalous reps of the diffeo group. So rather than being
inconsistent, the second type of gauge anomaly is in fact a
necessary condition for non-trivial consistency.
===
Subject: Re: Quantization without quantization
> covariant quantum theories (GCQT) and unitary
representations of the
> diffeomorphism group on a conventional Hilbert space.
Namely, if we
> have a GCQT, its Hilbert space carries a unitary rep of the
diffeo
> group. And if we have a unitary rep of the diffeo group,
the Hilbert
> space on which it acts can be interpreted as the Hilbert
space of
> some GCQT. Since all unitary quantum irreps of the diffeo
group are
> anomalous, apart from the trivial one, all interesting
GCQTs carry
> anomalous reps of the diffeo group. So rather than being
> inconsistent, the second type of gauge anomaly is in fact a
> necessary condition for non-trivial consistency.
Presumably the unitary reps in an interesting GCQT will be
constrained
by an anomaly cancellation condition?
===
Subject: Re: Quantization without quantization
> Presumably the unitary reps in an interesting GCQT will be
constrained
> by an anomaly cancellation condition?
Perhaps. Unfortunately, I don¹t understand how one can write
down a
well-deŽned BRST operator. There are three qualitatively
different
cases:
1. Finite-dimensional algebras. The BRST operator is always
well-
deŽned and nilpotent.
2. InŽnite-dimensional algebras living over a 1D manifold
(growth 1),
like Virasoro and afŽne Kac-Moody. The BRST operator is always
well-deŽned, but nilpotent only in special cases, like c = 26.
3. InŽnite-dimensional algebras of growth >= 2, like the
higher-
dimensional analogues of Virasoro and afŽne algebras. Here
the BRST
operators seems to be completely ill deŽned. The problem is
that
normal ordering would introduce an unrestricted sum over
transverse
modes.
If you do things in a Fourier basis on a 2D torus, say, the
modes
are labeled by momenta m = (m_1, m_2) in Z^2. We could deŽne
m > n
if m_1 > n_1. Normal ordering gives rise to a sum over all n,
0 < n < m, as is familiar from 1D. Hence we must sum over all
n such
that 0 < n_1 < m_1, and -inŽnity < n_2 < inŽnity. The second
sum
diverges.
This is the problem that prevented people from generalizing
the
Virasoro algebra to higher dimensions for 25 years. It can be
overcome by Žrst expanding all Želds in a Taylor
series around a marked, 1D curve, and truncating after some
Žnite
order. This gives us a non-linear realization of the
diffeomorphism
algebra on Žnitely many functions of a single variable, which
is
exactly where normal ordering works - there are no transverse
modes.
Unfortunately, I see no way to extend this trick to the BRST
operator, which led me to assert that one must live with the
anomaly. Be that as it is. My main point, however, is that in
order
to control the anomaly, you must Žrst be able to construct
it. LQG
cannot do that even in 2D, and therefore the LQG string is
probably
wrong. But neither LQG nor string theory (or Želd theory for
that
matter) can do that in 4D. The reason is that the anomaly
depends
on the marked curve that we Taylor expanded around.
In fact, it seems like people know how to canonically quantize
exactly those theories where the quantum representation
theory of
the constraint algebra is understood, typically conformal
theories
algebras of diffeomorphisms and gauge transformations in 4D
appear
to be very relevant.
===
Subject: String torsion constraints
Uma Mahanta and collaborators had made some estimates on
bounds on
propagating torsion using muon (g-2) experiments
(http://www.g-2.bnl.gov/index.shtml)
P. Das & U. Mahanta:
Torsion constraints from the recent precision measurement of
the muon
anomaly
hep-ph/0211137
as well as using LEP data (Mahanta&Raychudhuri,
hep-ph/0307350).
In the introduction of hep-ph/0211137 it says that the
authors want to
consider torsion as would follow from a non-vanishing H=dB
Želd strength
of
the string¹s Kalb-Ramond Želd. The action of that coupled to
fermions
should schematically read like
S = int (dB)^2 + bar psi D psi
where D is the Dirac operator with torsion ~H, i.e. D = y^m
d_m + H_lmn
y^lmn up to inessential prefactors (I write y for the Clifford
generators).
But Mahanta et al. instead use an action of the schematic
form (for totally
antisymmetric torsion)
S = int H^2 + (d*H)^2 + fermion coupling .
Does anyone know what the justiŽcation of this action is?
I have the impression that they are really thinking of the
standard action
of a massive 3 form, regarding the torsion 3-form as a
propagating Želd
instead of as the Želd strength of a 2-form B.
===
Subject: Re: String torsion constraints
Hi Urs,
Žrst of all - the word justiŽcation is probably not the best
word as
long as you work with string theory. In string theory you can
calculate
all these things - at least the equations of motion, and up
to a Želd
redeŽnition. See e.g. page 114 of Joe¹s book volume 1, and
pages 87, 91
of Joe¹s book volume 2 for the actions in the maximal
spacetime
dimensions in bosonic string and superstring theories,
respectively.
Second, these papers look confusing to me because they work
with the
B-Želd as torsion in four dimensions. The real physics of a
2-form
potential in 4 dimensions is that you can take its 3-form
Želd strength,
Hodge-dualize it, and obtain a one-form Želd strength of a
dual 0-form
potential. Therefore, physics of the B-Želd in 4 dimensions
is equivalent
to physics of a scalar. This scalar is called the axion - and
there are
many types of axions that can appear in various realistic
models.
(Axions have been proposed as dark matter candidates, and
especially as
solutions of the strong CP problem - why is the CP-violating
theta-angle
in QCD so small even though it does not have to be -
Peccei-Quinn
mechanism.)
> But Mahanta et al. instead use an action of the schematic
form (for
totally
> antisymmetric torsion)
> S = int H^2 + (d*H)^2 + fermion coupling .
I¹ve seen this action neither in the paper you mentioned nor
anywhere
else. d*H is roughly *Box(B). This term has a different
dimension, and
would have to include a prefactor of order alpha¹ -
relatively to the
main kinetic term (H^2). I think it¹s plausible that it
appears as an
alpha¹-correction, but it is irrelevant at low energies. Why
do you care
about it?
Best
Lubos
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Re: String torsion constraints
Lubos Motl <motl@feynman.harvard.edu> schrieb im Newsbeitrag
> Žrst of all - the word justiŽcation is probably not the
best word
as
> long as you work with string theory. In string theory you
can calculate
> all these things - at least the equations of motion, and up
to a Želd
> redeŽnition. See e.g. page 114 of Joe¹s book volume 1, and
pages 87, 91
> of Joe¹s book volume 2 for the actions in the maximal
spacetime
> dimensions in bosonic string and superstring theories,
respectively.
Yup. And because these authors use something different I was
wondering what
they thought should be the justiŽcation for doing so.
> Second, these papers look confusing to me because they work
with the
> B-Želd as torsion in four dimensions. The real physics of a
2-form
> potential in 4 dimensions is that you can take its 3-form
Želd strength,
> Hodge-dualize it, and obtain a one-form Želd strength of a
dual 0-form
> potential. Therefore, physics of the B-Želd in 4 dimensions
is
equivalent
> to physics of a scalar. This scalar is called the axion -
and there are
> many types of axions that can appear in various realistic
models.
I know that you dualize to get the axion. But that¹s just
rewriting. It
does
not change the fact that the fermions see a torsion, whether
you write that
as d B or as * d chi
> S = int H^2 + (d*H)^2 + fermion coupling .
> I¹ve seen this action neither in the paper you mentioned
nor anywhere
> else.
Their S^mu is *H and their S^mu nu is d * H.
> Why do you care about it?
Because I am wondering about phenomenological consequences of
torsion
effects on fermions. I am not the only one. There are a
couple of paper on
that, but none of them that I have seen so far seem to
correctly deal with
the string theory formalism.
===
Subject: Re: New book by Zwiebach
I don¹t think its appropriate to teach undergrads (much less
sophomores)
this material. They should be learning the things that are
tried and
true, down to 11 decimal places.
[Moderator¹s note: Even if someone thought that string theory
is *not*
true,
the book shows many different physical situations that
require both
physical and mathematical tools that are useful nearly
everywhere in
physics.
Moreover, if we were only teaching dead subjects that have
already
been
completed, the excitement of the students would be
signiŽcantly reduced.
It¹s just a great idea to show them basics of the
cutting-edge research.
This basic course of string theory is also an excellent
opportunity for
the readers (and students) to reŽne their experience with
other
subjects in physics, especially special relativity,
electromagnetism,
quantum mechanics, and statistical physics. Incidentally,
only QED, the
non-perturbatively inconsistent quantum Želd theory of light
and matter,
has been tested with the accuracy you mentioned. QCD, the
asymptotically
free non-perturbatively Žnite theory, expecting a Nobel prize
on Tuesday
or next year, is only tested up to a 1% precision or so, for
example.
If I summarize, Barton did a great job, and his book truly
deserves to be
the topseller among all textbooks (it¹s been on rank 1,200 at
amazon.com, which is really not bad for a textbook). LM]
Consider that perhaps only half of them go to grad school, the
remaining lot need to be learning the successful applications
of the
scientiŽc method, and how to be skeptics.
[Moderator¹s note: What you say is important, but there are
still many
other subjects that should be doing it. But it is also
important to make
the students understand that some theories are under
construction even
today and physics has not ended with QM or QED - but that
these theories
must
follow strict rules of mathematics and logic much like the
old ones.
Especially for those who will not become graduate students in
theoretical
physics, it is important - I think - that they will have an
idea how the
current research looks like. And string theory is, of course,
the most
logically rigid new theoretical structure the physicists
study today -
and
among the theories under development, it is obviously the
theory with
the strongest links with other important structures in
physics, including
those that you had in mind. LM]
We shouldnt¹ be indoctrinating them with highly advanced
material that
conceptually changes every 5 years (read astrophysics and
quantum
gravity), ...
[Moderator¹s note: There is virtually nothing that can change
about a book
by Zwiebach in next 5 years. We can learn other important
ideas, but we
will hardly undo the insights described in this book. I don¹t
exactly
know what you mean by the periodic 5-year conceptual
revolutions in
astrophysics, but there are many other statements in your
posting whose
origin is very unclear to me, so I won¹t ask you about all of
them.
Let me summarize this part: among the theories under
consideration,
the basics of string theory remain the most reliable insight.
Everything else can change, dualities modify our idea about
nonperturbative physics of quantum gravity or whatever - but
the free
relativistic string is nearly guaranteed to remain an
important physical
system that should be taught. LM]
... that sorta defeats the fundamental purpose of the
education of
science, not to mention confuses issues that they may not
have even seen
before (I didn¹t even have quantum mechanics 1 until junior
year at a
level beyond the usual hand wavey experimental successes).
[Moderator¹s note: I Žrst learned about Maxwell¹s equations
from a paper
by Einstein about the Maxwell¹s system in general relativity
when I was
16, and you can see that I survived. The feeling that one
studies
something at the cutting edge is very important for the
person¹s
curiosity about the subject. In my opinion, science is not a
collection
of completed religious dogmas that don¹t allow any
extensions, and it
is still making clear progress - and the understanding of
this fact is,
I believe, one of the fundamental purposes of science
education. LM]
Consider that even the rudiments of Želd theory is rarely
taught at a
phenomenological level until senior year.
[Moderator¹s note: Barton¹s choice of the topics is very
reasonable.
Classical strings are a perfect example of classical
mechanics. Instead
of many convoluted exercises in classical mechanics, he can
study the
relativistic string as an example of the 1+1-dimensional Želd
theory.
In some sense, the string is *simpler* than other things we
can teach.
Moreover, it is a Lorentz-invariant theory, and a great
exercise in
relativity - there are not too many interesting nontrivial
exercises
like that. He quantizes the strings in the light-cone gauge -
which
allows him to avoid ghosts of all types - and the light-cone
gauge
spectrum is a great context to crystallize the knowledge of
commutators,
harmonic oscillators in quantum mechanics, and so forth. LM]
However it should be a Žrst year elective graduate level
class, at
least in principle, with levels 2 and 3 for those who are
interested in
subsequent semesters. Unfortunately, not every school offers
courses
like that, which is highly irratating.
But sophomores, come on! How much can you really teach them
beyond a
pseudo religious handwavey type of spiel.
[Moderator¹s note: You obviously have not read a single page
of that book
because otherwise you could never say a nonsense like that.
Even for
those who don¹t want to believe string theory, the book is a
perfect
collection of great arguments and exercises training the
concepts of
mechanics, Želd theory, quantization, and so on. Another
sourball
could have written a posting like yours before Barton
actually started
with
the experiment - and this sourball could have killed this
idea. However,
today we are in a different situation. Barton¹s experiment
has already
been proved to be a very good idea experimentally, and your
hostile
speculations have already been ruled out. LM]
-------------------------------------------------------------
-----------
This post submitted through the LaTeX-enabled
physicsforums.com
To view this post with LaTeX images:
http://www.physicsforums.com/showthread.php?t=33905#post327490
===
Subject: Re: New book by Zwiebach
> Even if someone thought that string theory is *not* true,
> the book shows many different physical situations that
require both
> physical and mathematical tools that are useful nearly
everywhere in
physics.
Sure, that is Žne, but they can get those same tools in
regular
classes.
> Incidentally, only QED, the
> non-perturbatively inconsistent quantum Želd theory of
light and
matter,
> has been tested with the accuracy you mentioned.
Err you can Žnd examples in statistical mechanics, optics,
žuid
mechanics, general mechanics, žuid mechanics, etc etc where
the
(read QED).
> And string theory is, of course, the most
> logically rigid new theoretical structure the physicists
study today
- and
> among the theories under development,
Maybe, sure why not. But again it begs the question.. Why
aren¹t we
teaching the cutting edge intro classes in other areas like
statistical mechanics.. Like say the BCS theory of
superconductors.
Precisely b/c its *hard* and the amount of material needed to
understand things fully requires more than 1 year of freshman
physics.
> There is virtually nothing that can change about a book
> by Zwiebach in next 5 years.
Fine, 5 years is too broad a stroke. Still other Želds like
cosmology have been changing so rapidly, its hard to keep
pace with
the current thinking. Consider, when I learned relativity
(also at
the age of 15), Inžation wasn¹t even taught. Black holes had
scarce
empirical evidence.. Most people still were convinced we were
living
in a closed universe, hell most people didn¹t even know what
a D-Brane
was. I¹d say the paradigm has shifted slightly in the last 10
years
since then. Likewise, I would assume quantum gravity is
equally as
fast paced and active a Želd.
[Moderator¹s note: I just wanted to say that Zwiebach¹s book
is not
a book about some over-specialized speculations. It is a book
about
serious stuff related to physics of strings, and the
mathematical
methods and steps explained in this book are - and will be -
undisputable. LM]
> In my opinion, science is not a collection
> of completed religious dogmas that don¹t allow any
extensions, and it
> is still making clear progress - and the understanding of
this fact is,
> I believe, one of the fundamental purposes of science
education. LM]
I see what you are saying, but I don¹t quite agree. Respective
theories like Maxwell¹s equations ARE religious dogma. They
won¹t
change in 5 years, 1000 years from now, or 10000 years from
now. They
are simply the way nature is at some suitable approximation of
validity. Now, curiousity of the cutting edge is important,
and its
nice to throw in some examples here and there to tantalize
people.
But a full on course, without the background material.. mmm
> But sophomores, come on! How much can you really teach them
beyond a
> pseudo religious handwavey type of spiel.
> You obviously have not read a single page of that book
> because otherwise you could never say a nonsense like that.
Even for
> those who don¹t want to believe string theory, the book is
a perfect
> collection of great arguments and exercises training the
concepts of
> mechanics, Želd theory, quantization, and so on.
Well you are correct, I admit I have never read a page of
that book
(id love too actually, now that I am quite well versed in
texts like
Polchinski)
You know, I considered quantum mechanics 1 pseudo religious
handwavey
type of spiel as well when I was in college. Why? B/c I had
already
taken relativity, and Schroedingers equation is manifestly non
covariant. It wasn¹t until Dirac¹s eqns, Želd theory et al
that
things all of a sudden made sense in a somewhat rigorous way.
Here
you are teaching string theory, without knowledge of things
like
conformal Želd theory. How seriously do you think people are
going
to take things? Even if the theory deep down is fundamentally
sound,
what you teach them is literally replete with conceptual
holes.
So I mantain, if you are going to teach something with
conceptual
holes to beginners, might as well start from the basics.. Like
classical mechanics, and progress onwards, in a logical
fashion.
Still, point taken, his seems to be a popular success story.
===
Subject: Congratulations to Gross, Politzer, Wilczek
Today I woke up a bit early, to see how they have decided at
http://nobelprize.org/
They decided correctly at last! We¹ve been guessing Gross,
Politzer, and
Wilczek as the strongest candidates at least for Žve years.
This time was
different, and our belief was strong.
Gross and Wilczek in particular are continuing to be the
leaders of the
Gross is the director of the Kavli Institute for Theoretical
Physics in
Santa Barbara.
The reason why this posting is not off-topic is that David
Gross is also -
I believe - the Žrst string theorist awarded by the Nobel
prize. (Among
hundreds of his important papers, he is a co-discoverer of
the heterotic
string.) Well, the prize is not exactly for string theory
this time, but
at least, it is for something that may be dual to a string
theory. :-)
You can read about the history of asymptotic freedom - that
was
freedom (well, now it¹s over 30 years)
http://arxiv.org/abs/hep-th/9809060
We hope that the stringiness of the awarded discovery will be
better next
time; the beginnings are often modest, and string theory is
the best
example. ;-)
Congratulations, Gentlemen, and thank you for your numerous
contributions
and excitement!
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Problem with Polchinski
I have been running into subtle problems with the Polchinski
book treatment of conformal Želd theory. I cannot seem to
Žgure
out why the following statement is correct:
Since the variation of the path integral w.r.t. the metric
is given by an expectation value of the E-M-tensor as follows:
delta <...>_g = int sqrt{g} h_{ab} <T^{ab}...>
where h_{ab} = delta g_{ab},
the *second-order* variation (see 3.4.22, p 94) is given
by a double integral with two insertions of T:
int d^z sqrt{g(z)} int d^z¹ sqrt g(z¹)
h_{ab}(z) h_{cd}(z¹) <T^{cd}(z¹) T^{ab}(z)>.
I agree with the Žrst formula when ... denotes operators
that do not explicitly depend on the metric.
However, when I try to verify the second formula, it seems to
me
that he has forgotten that
T_{ab} = del_a X del_b X - half g{ab} g^{cd} del_c X del_d X
really *does* depend on the metric,
so that one should really have an *extra* term in the second
variation
int sqrt{g} h_{ab} <delta T^{ab}>
since delta T^{ab} is not in general 0.
[Moderator¹s note: T^{ab} is not zero in general, but have
not you
considered the possibility that h_{ab} T^{ab} *is* zero in
general?
It¹s called tracelessness and holds for all conformal Želd
theories.
For example, with the deŽnition of T above, the two terms
cancel. LM]
Am I missing something? I suspect I am, since Polchinski¹s
(incorrect?) formula for multiple insertions is actually
taken by some other authors as an axiomatic property of T.
Any help would be appreciated.
J.E.
===
Subject: Re: Problem with Polchinski
I apologize, Joan. You are absolutely correct. This is a
small issue with
Polchinski¹s book. Your observation leads to new terms that
are only
non-vanishing for z=z¹ (which don¹t affect the questions he
wants to
study), and Polchinski says the following:
p. 94 (12/31/98)*: In eqs. 3.4.21 and 3.4.22, contact terms
(additional
terms at z = z¹, as well as ambiguities in various quantities
at that
point) are (deliberately) ignored: the relation between c and
a_1 is
See http://theory.itp.ucsb.edu/~joep/errata.html
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Re: Problem with Polchinski
> [Moderator¹s note: T^{ab} is not zero in general, but have
not you
> considered the possibility that h_{ab} T^{ab} *is* zero in
general?
> It¹s called tracelessness and holds for all conformal Želd
> theories. For example, with the deŽnition of T above, the
two terms
cancel.
> LM]
indeed zero. However, I used the notation h_{ab} = delta
g_{ab},
the variation of g, and delta T^{ab} for the variation of T
with
respect to g. Then the second order term
delta g_{ab} delta T^{ab}
does not seem to be zero when I simplify it.
J.E.
[Moderator¹s note: You probably meant (delta g_{ab}) T^{ab}
without
delta before T? One must be careful about all these details.
My
feeling is, and please don¹t get insulted, that Polchinski
and others
were more careful than you, and they deŽnitely varied
everything
that should be varied. When I look at your question, I am
more puzzled
than before. Why do you vary T^{ab} once again? T^{ab} is
already
the result of the variation (of the matter part of the
action) with
respect to g_{ab}. It is not input to vary: it is already the
coefŽcient
of the result, by deŽnition, and it should not be varied
twice.
Does it make sense? LM]
===
Subject: Standard Model from String Theory
3 scale inputs plus the symmetry group, giving seven inputs.
It is
typical of group-based GUT theories. Surely you [Tony Smith]
can even
predict the disintegration rate of proton (no joking, they
do).
Perhaps your question in this forum could be, if string
theory has
something to say about the group. As far as I understand, the
answer
is negative because moduli spaces let you choose between a
lot of
different groups.
Isn¹t getting the standard model from string theory what lots
of
people have tried to do in lots of very different ways? The
original
popular way was to use an E6 subgroup of E8xE8. Smith gets E6
from E7.
Is Smith forced into a particular group cause his model is a
bosonic
string one? Lee Smolin has tried to use a single exceptional
group to
get M-theory. Smolin interestingly started with a bosonic
stringlike
26 dimensions and tried to use the 16 extra to get
supersymmetry. In
the old days didn¹t they try to use the extra 16 to get the
standard
model bosons? Smith uses the extra 16 to get standard model
fermions.
It¹s amazing how the same math can be used so differently. I
like
Smith¹s interpretation but I¹m not sure even Smith would
agree with my
reasons. My reasons kind of fall in the Lubos Motl mind of god
aestetics category. The root vector geometry for these 16
vertices
(actually 32 vertices since the dimensions are complex) look
more like
fermions to me. This has to do with them seeming to group
nicely into
up vs. down and the bosons being more naturally down in the
SU(5)-like
subgroups. Smith by the way does have exactly the same proton
decay
rate as minimal SU(5) GUT. By including the standard model,
Smith is
able to use diffusion equations on lattices or complex
domains to get
usually just uses lattices for this.
===
Subject: Re: Standard Model from String Theory
> Isn¹t getting the standard model from string theory what
lots of
> people have tried to do in lots of very different ways? The
original
> popular way was to use an E6 subgroup of E8xE8. Smith gets
E6 from E7.
> Is Smith forced into a particular group cause his model is
a bosonic
> string one?
Just a couple of trivialities: the couplings in the Standard
Model are
therefore we need complex representations (those that are
inequivalent to
their complex conjugates). E_6 is the only exceptional group
whose compact
form has any complex representations (the complex conjugation
follows
from the symmetry of the E_6 Dynkin diagram). Therefore E_6
is the only
viable group for Grand UniŽcation.
In the models based on heterotic string theory by David Gross
et al., this
E_6 - or potentially smaller groups of it such as SO(16) -
are obtained as
the subgroup of E_8 which appears in heterotic string theory
automatically. But the check is not just that E_6 is the
correct subgroup
of E_8. Even the correct representations appear - 248 of E_8
decomposes
under E_6times SU(3) - where SU(3) is the centralizer of E_6
and vice
versa (in both cases inside E_8) - as
248 = (78,1) + (27,3) + (27*,3*), (1,8)
If you compactify the heterotic string on Calabi-Yau, the
adjoint (78) of
E_6 is of course broken to the unbroken group; the fermions
appear from
the triplets - the triplets of SU(3) - 3 and 3* - are
actually reduced to
1 by the Calabi-Yau magic, but it is still important that the
fermions
transform as 27 of E_6, which is a realistic (complex)
representation of
E_6 for the fermions. (It contains the chiral complex spinor
16 under the
subgroup SO(10), and this 16 is exactly what we want to
reproduce the 15
Weyl spinors of one generations of quarks and leptons, plus a
single
extra right-handed neutrino.) Well, everything goes through
if I
imagine
that E_8 is broken to E_6 via E_7 as an intermediate step -
and therefore
a model with a E_7 starting group could give the right
representations,
too, except that I don¹t know any good theory that only has
E_7 at the
beginning.
> Lee Smolin has tried to use a single exceptional group to
> get M-theory. Smolin interestingly started with a bosonic
stringlike
> 26 dimensions and tried to use the 16 extra to get
supersymmetry.
A well-known non-stringy colleague of mine has recently
rejected a paper
that claimed to have obtained a spacetime supersymmetric
model from
bosonic string theory. If someone claims that there is a
serious way to
get spacetime SUSY from bosonic string theory, I am eager to
hear about it
(because the possible relations between the superstring and
the bosonic
string have always excited me) - but be prepared that I think
that
extraordinary claims require extraordinary evidence. ;-)
> In the old days didn¹t they try to use the extra 16 to get
the
> standard model bosons?
Not sure whether you mean successful research or unsuccessful
speculations. The success story is the heterotic string in
which you can
derive the gauge group E_8 x E_8 (or SO(32)) from the
16=26-10 extra
chiral bosons, as long as you use the correct, modular
invariant theory,
and you Žnd all the wrapped/momentum states that produce the
W-bosons
(those outside the Cartan subalgebra).
> Smith uses the extra 16 to get standard model fermions.
That does not really sound right. The extra 16 bosons simply
must live on
the even self-dual lattice, and they uniquely lead to the two
heterotic
string theories. Moreover, there are translation symmetries
for them, so
the theory is guaranteed to have at least U(1)^{16} as the
gauge group
from the very beginning. Does he make some orbifolds of the
chiral bosons,
or chiral bosons with linear dilaton, or something like that?
I¹ve been
thinking about such additional options recently, but
certainly not in
connection with the Standard Model fermions. ;-)
> It¹s amazing how the same math can be used so differently.
I like
> Smith¹s interpretation but I¹m not sure even Smith would
agree with my
> reasons. My reasons kind of fall in the Lubos Motl mind of
god
> aestetics category. The root vector geometry for these 16
vertices
> (actually 32 vertices since the dimensions are complex)
look more like
> fermions to me.
I am not sure what is needed for a root vector to look like a
fermion
;-), but mathematically, the ground state in the heterotic
string lattice
has the same statistics as the zero-momentum state. To change
its
statistics, you must add some cocycles, and to make it
consistent, you
must simultaneously redeŽne your spacetime rotations. Can he
get the
superstring or something related by deŽning the physical
Lorentz group as
a diagonal group acting on two groups of X¹s on the
worldsheet? That
certainly sounds exciting and similar to many working things
in physics,
but does it really work here? Is it really a conformal Želd
theory that
leads to a realistic low-energy physics in spacetime?
_____________________________________________________________
_______________
__
E-mail: lumo@matfyz.cz fax: +1-617/496-0110 Web:
http://lumo.matfyz.cz/
eFax: +1-801/454-1858 work: +1-617/384-9488 home:
+1-617/868-4487
(call)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^
^^
===
Subject: Does n-Brane theory conžict with Big Bang model of
the universe?
Does n-Brane theory conžict with the Big Bang model of the
Universe
and instead imply a Big Collapse or a Big Squish?
If one thinks of the universe as a single self-contained
entity, then
the Universe is exactly one Universe wide and has always been
so,
and everything inside of it is instead shrinking. The reason
the
Universe appears to be expanding is because three-dimensional
stuff
inside it is in fact collapsing, as have the other
n-dimensions
outlined in string theory.
The easist way (for me, at least) to picture this is if one
has a
ruler that is exactly one meter long. When you measure
yourself, you
are some multiple of one meter tall. However, if both you and
the
measuring stick are shrinking, it appears that everything
else is
getting farther away, while you are remaining the same size.
(Eventually, you and the meter stick shrink to a singularity.)
This would explain why everything in the Universe appears to
be
receeding from us. It¹s not really receeding- it¹s
collapsing. It also
eliminates the idea that the Universe is expanding into
nothing, which
always seemed counter-intuitive to me.
Any comments would be appreciated.
Charles Hoffmann
charleshhoffmann@comcast.net
===
Subject: Re: Standard Model from String Theory
> Lee Smolin has tried to use a single exceptional group to
> get M-theory. Smolin interestingly started with a bosonic
stringlike
> 26 dimensions and tried to use the 16 extra to get
supersymmetry.
> A well-known non-stringy colleague of mine has recently
rejected a paper
> that claimed to have obtained a spacetime supersymmetric
model from
> bosonic string theory. If someone claims that there is a
serious way to
> get spacetime SUSY from bosonic string theory, I am eager
to hear about
it
> (because the possible relations between the superstring and
the bosonic
> string have always excited me) - but be prepared that I
think that
> extraordinary claims require extraordinary evidence. ;-)
Here is the link to Lee Smolin¹s paper on this. He is doing
very much
the same thing as Smith with added addition of looking for
SUSY:
http://xxx.lanl.gov/PS_cache/hep-th/pdf/0104/0104050.pdf
> In the old days didn¹t they try to use the extra 16 to get
the
> standard model bosons?
> Not sure whether you mean successful research or
unsuccessful
> speculations. The success story is the heterotic string in
which you can
> derive the gauge group E_8 x E_8 (or SO(32)) from the
16=26-10 extra
> chiral bosons, as long as you use the correct, modular
invariant theory,
> and you Žnd all the wrapped/momentum states that produce the
W-bosons
> (those outside the Cartan subalgebra).
had in mind and it looks like you¹ve supplied the last
sentences for
that story: Accordingly, if the Yang-Mills forces, such as
electromagnetism, are included in a string theory, they must
be
uniŽed with gravity in an intimate way. A kind of theory in
which the
YangMills forces can be associated with closed strings was
formulated
by David J. Gross, Jeffrey A. Harvey, Emil J. Martinec and
Ryan Rohm
of Princeton University. Such a theory is known as heterotic,
and it
is the most promising kind of superstring theory developed so
far. Its
construction is quite strange. The charges of the Yang-Mills
forces
are included by smearing them out over the entire heterotic
string.
Waves can travel around any closed string in two directions,
but on a
heterotic closed string the waves traveling clockwise are
waves of a
10-dimensional superstring theory; the waves traveling
counterclockwise are waves of the original, 26-dimensional
string
theory. The extra 16 dimensions are interpreted as internal
dimensions
responsible for the symmetries of the Yang-Mills forces.
> Smith uses the extra 16 to get standard model fermions.
> That does not really sound right. The extra 16 bosons
simply must live on
> the even self-dual lattice, and they uniquely lead to the
two heterotic
> string theories. Moreover, there are translation symmetries
for them, so
> the theory is guaranteed to have at least U(1)^{16} as the
gauge group
> from the very beginning. Does he make some orbifolds of the
chiral
bosons,
> or chiral bosons with linear dilaton, or something like
that? I¹ve been
> thinking about such additional options recently, but
certainly not in
> connection with the Standard Model fermions. ;-)
Yes, this is how Tony Smith describes it on his website:
The following is my proposal to use the exceptional Lie
algebra
E6(-26), which I will for the rest of this message write as
E6, to
introduce fermions into string theory in a new way, based on
the
exceptional E6 relations between bosonic ve