|Jul24-12, 12:44 AM||#18|
String theory today
marcus, as a non-expert in string theory I don't dare to answer these questions based on headlines; abstracts would be helpful
|Jul24-12, 01:29 AM||#19|
If anybody wants, they can grade the first day talks (which have their PDF posted) and send me PM. I would keep the scoring anonymous. Or Tom you could be the scorekeeper.
Or we could set up a poll? I'm getting sleepy. It is nearly 11:30 PM. Long day. Maybe we can decide how to do this tomorrow.
I did notice that there were almost no talks about understanding how the big bang might work. There was something about non-singular cosmology which sounded like it might be.
I'll get back to this tomorrow.
|Jul24-12, 09:03 AM||#20|
Videos are now available for the Monday talks.
So, for example, Strominger's talk can be heard, which I expect will make the slides more comprehensible.
EDIT, yes! It really does. I just watched the full talk and some of the Q&A following it.
The split screen video format is nice visually. The only drawback is you can't see a moving dot on the slide where he is pointing to something. You have to guess what part of the slide he's indicating, but that's usually possible.
It's a good talk! He makes no reference to Hartle Hertog Hawking recent paper. He's really interested in deSitter space come hell-or-high-water, and throwing everything he's got at it. Nice to see.
Apparently the 30 minute timeslot the regular speakers get is supposed to be just 20 minutes for the talk leaving 10 minutes for Q&A discussion.
EDIT: A paper relating to Strominger's talk came out today:
The Wave Function of Vasiliev's Universe - A Few Slices Thereof
Dionysios Anninos, Frederik Denef, Daniel Harlow
(Submitted on 23 Jul 2012)
We study the partition function of the free Sp(N) conformal field theory recently conjectured to be dual to asymptotically de Sitter higher-spin gravity in four-dimensions. We compute the partition function of this CFT on a round sphere as a function of a finite mass deformation, on a squashed sphere as a function of the squashing parameter, and on an S2xS1 geometry as a function of the relative size of S2 and S1. We find that the partition function is divergent at large negative mass in the first case, and for small $S^1$ in the third case. It is globally peaked at zero squashing in the second case. Through the duality this partition function contains information about the wave function of the universe. We show that the divergence at small S1 occurs also in Einstein gravity if certain complex solutions are included, but the divergence in the mass parameter is new. We suggest an interpretation for this divergence as indicating an instability of de Sitter space in higher spin gravity, consistent with general arguments that de Sitter space cannot be stable in quantum gravity.30 pages plus appendices, 6 figures
|Jul25-12, 10:33 AM||#21|
Videos are now available for the Monday and Tuesday talks.
Since we just turned a page, and folks may not have seen it, I'll repost the schedule:
Survey talks for which an hour is scheduled are highlighted. Others have 30 minute timeslots. Strominger kept his talk to 20 minutes so there would be an ample 10 minutes for audience questions and discussion. Note that Witten and Arkani-Hamed are among the Tuesday speakers whose videos are now online.
J. Schwarz Opening Lecture (I)
G. Veneziano Opening Lecture (II)
A. Strominger Progress in dS/CFT
E. Silverstein RG and unitarity in spacetime-dependent QFT
F. Alday Mixed correlators in N=4 SYM
A. Karch Recent Applications of the Gauge/Gravity Correspondence to QCD and Condensed Matter Physics
S. Kachru New Horizons in Finite Density Field Theory and String Theory
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
E. Rabinovici (In) Stabilities and complementarity in AdS/CFT
X. Yin Higher Spin Holography
M. Gaberdiel Minimal Model Holography
E. Witten Superstring Perturbation Theory Revisited
A. Castro Path integrals in 3D gravity
J. Maldacena Constraining theories with higher spin symmetry
J. Carrasco Generic multiloop methods for gauge and gravity scattering amplitudes, a guided tour with pedagogic aspiration
N. Arkani-Hamed Scattering Amplitudes and the Positive Grassmannian
O. Schlotterer Hidden simplicity in superstring amplitudes
F. Cachazo Gravity in Twistor Space
A. Uranga Update on string phenomenology
M. Cvetič Non-perturbative Effects in F-theory Compactifications
B. Zwiebach Glimpses of Double Field Theory Geometry
J. Heckman Covariant Non-Commutative Geometry From String Theory
L. Anderson New Aspects of Heterotic Geometry and Phenomenology
S. Dimopoulos What has the LHC done to Theory?
S. Kortner Status and latest results of the LHC
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
I. Antoniadis Aspects of string phenomenology in the new LHC era
N. Seiberg Chern-Simons Contact Terms
H. Nicolai Alternative approaches to quantum gravity: a brief survey
B. Freivogel Predictions from Eternal Inflation
C. Gomez Black holes as graviton condensates at the critical point of a quantum phase transition
A. Polyakov Quantum Instability of the de Sitter space
C. Vafa Topological Strings and Their Diverse Applications
M. Aganagic Knots, Mirror Symmetry and Large N Duality
D. Gaiotto Domain walls and RG flows
M. Yamazaki Networks, Quivers and 3-manifolds
T. Dimofte Class R: A User's Guide
Z. Komargodski Comments on the Renormalization Group and Diverse Applications
C. Bachas AdS4/CFT3 and Gravity Localization
L. Rastelli Bootstrapping the Superconformal Index
C. Kounnas Non-singular Superstring Cosmologies
H. Ooguri Conference Summary
D. Gross Outlook and Vision
Tom's question is an important one to be asking (sampling the talks so far has brought that point home for me.)
Let me as a question: which talks address physical isues (like quantum gravity, big bang, black holes, particles and symmetries, unification, ...) and which talks address "home-made" problems of string theory?
|Jul25-12, 10:40 AM||#22|
Thanks for posting these Marcus! I'm going to start watching them now.
|Jul26-12, 06:36 PM||#23|
Glad to hear someone else is interested! I continue watching bits and pieces. Witten's talk seemed unlikely to arouse much enthusiasm. It was about perturbative string, fixing some odds and ends at the level of detail. He didn't give much motivation for going back to an earlier era.
The Wednesday talk I wanted to watch was titled *Update on String Theory Phenomenology* by Angel Uranga.
It was not about phenomenology as I understand it--I think of phenomenology as figuring out ways to base prediction of new physical phenomena so that you can test. Very little of the talk was concerned with that.
It seemed to me to be more about problems internal to the String theory program. But you can watch for yourself.
At MINUTE 40 he started the "de Sitter and moduli stabilization" part of his talk, if you want to skip to it. Just drag the time button.
At MINUTE 50 he started the short section on *Heterotic Orbifolds*
At Minute 51 *Other CFT models*
At Minute 52 *Higgs*
At Minute 58 he showed his conclusion slide and ended the talk.
There were a couple of minutes of Q&A and the session ended at minute 62 (1:02 h)
Uranga and Ibañez have a new (2012) book out called *Introduction to String Theory Phenomenology*. I guess we should say that this defines the field: "they wrote the book on it."
You can browse the table of contents at the Amazon page. Much of the ToC corresponds to the topics covered in the talk.
So far the talk that I found most interesting (from my limited perspective) has been that of Strominger on dS/CFT---which essentially requires shifting to a new non-Einstein theory of gravity called *Vasiliev* gravity. It is a serious and bold move (or so it seems to me). Respectable whether or not it succeeds in the end. As I think I said earlier, he made no reference the HartleHawkingHertog paper.
The video is the best looking and most convenient I've ever seen, for a conference. You can drag the time button to any place in the talk and it will catch up and start there with almost no waiting.
|Jul27-12, 12:37 AM||#24|
- no supersymmetric measure (like d4p in ordinary QFT) known beyond a few loops
- therefore no definition of higher-loop amplitutes
- no proof of finiteness of higher-loop amplitutes
- no proof of convergence of the perturbation series
Did he address something?
Would be nice to see your comments
|Jul27-12, 09:33 AM||#25|
Here is the PDF of the slides. The slides have much or all of what was said written out (the talk consisted largely of recitation exactly duplicating the slides word for word.)
You can see what was covered. All the papers referred to are from the 1980s. (Except for one or two from 1979 or so) and are about perturbative string.
He found a slight imperfection or incompleteness in the 1980s work. It was overlooked that certain tadpoles might acquire mass. The talk was devoted to correcting this omission, and thus putting the 1980s results on a firmer footing.
I'm afraid you need to look at the PDF, or perhaps watch some of the talk, in order to get a more reliable impression. The talk is only a few minutes long. AFAICS he did not address the topics you mentioned except in a limited way by implication (if there was a flaw in earlier work then fixing it surely contributes to establishing finiteness and convergence!)
The final slide (which serves to sum up what the talk has covered) was:
When one can show that the gravitino cannot gain a mass in perturbation theory – for instance in R10 – this relation should (when combined with what was discovered in the 80’s and a few details that we haven’t had time for today) – remove the very slight unclarity that has surrounded superstring perturbation theory.
I'd appreciate yours and other's comments--on this and other talks. Your comments are apt to be more insightful and informative than mine.
|Jul27-12, 12:24 PM||#26|
In the superstring, the tachyon is absent. Furthermore, in the cases where supermoduli space is split, the integration over the odd moduli contributes to the measure over even moduli. We expect IR divergences to be related to the same phenomena as in the bosonic string. In the 1-loop and 2-loop vacuum cases, these divergences vanish after summing over the spin-structures. If the supermoduli space is not split, you can't sum over spin structures until you've integrated over the supermoduli. Witten's work is an attempt to investigate these IR divergences in this general case.
|Jul27-12, 12:29 PM||#27|
Witten hinted he had a paper in preperation regarding details of the super Riemann surface at 2 loops, which did not use the same trick that Chen and Phong utilized.
Consequently its not hard to imagine that it might allow a new proof of the finiteness of the 2 loop amplitude and that further it might generalize more readily to the higher orders.
|Jul27-12, 02:07 PM||#28|
But alas, what sense does it make to discuss this here.
|Jul27-12, 02:08 PM||#29|
|Jul27-12, 03:05 PM||#30|
|Jul28-12, 04:28 AM||#31|
OK, seems to be a very subtle and rather unphysical issue. Nobody would ever calculate a 27-loop superintegtral even if the whole series would be finite ;-)
The question is why Witten addresses these issues today? What's the reason for the interest in these perturbative calculations?
|Jul28-12, 07:48 AM||#32|
Instead of agomizing about what he said or not and trying to read patterns in the coffee mug, why not just sitting back and wait for the paper to come out?
edit: well probably it is easier to read off the purported decline of string theory from the coffee mug, rather from actual research. So why dont you keep on going.
|Jul28-12, 10:11 AM||#33|
I just tried the video link for David Gross's "Outlook and Vision" talk
and it did not work.
BTW on the overall list of video links it says a one-minute segment at the beginning of the talk is missing:
Folks might want to watch some of Ooguri's "Conference Summary":
I just watched it. To the extent I could judge (not being at the conference) he did an excellent job. Highly informative, concentrated, fast, upbeat. He paraphrased Winston Churchill's speech "we shall fight on the X, we shall fight in the Y, we shall..." This fine paraphrase of of Churchill's morale-boosting determination in a dark hour came at minute 18 of Ooguri's talk. Strings 2013 will be at Seoul, 2014 in Princeton, 2015 in Bangalore. Ooguri gave a lightning montage of thumbnails of ALL the talks: lots of work went into the visuals and the delivery was excellent. Five stars.
I just tried again to get Gross's talk and it is still not coming up.
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