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## 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

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 Quote by tom.stoer marcus, as a non-expert in string theory I don't dare to answer these questions based on headlines; abstracts would be helpful
The full set of slides of each talk seems to be posted after the talks of the day are over. So we will be able to see, day by day, which talks address the realworld problems that you mentioned. (I think.) Maybe grade them on a scale 1 to 5? Where 5 is for all out tackling what has to be done and 1 is for only solving "home made" problems?
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.

 Recognitions: Gold Member Science Advisor Videos are now available for the Monday talks. http://www.theorie.physik.uni-muench...012/index.html 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: http://arxiv.org/abs/1207.5517 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
 Recognitions: Gold Member Science Advisor Videos are now available for the Monday and Tuesday talks. http://www.theorie.physik.uni-muench...012/index.html 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. http://wwwth.mpp.mpg.de/members/stri...ram/talks.html Monday 23 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 Tuesday 24 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 Wednesday 25 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 Thursday 26 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 Friday 27 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? ===
 Thanks for posting these Marcus! I'm going to start watching them now.

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 Quote by marcus Witten's talk ... was about perturbative string, fixing some odds and ends at the level of detail.
I am aware of:
- 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

What else?

 Recognitions: Gold Member Science Advisor 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.) http://wwwth.mpp.mpg.de/members/stri...day/Witten.pdf 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: ==quote== 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. ==endquote== 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.

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 Quote by tom.stoer I am aware of: - no supersymmetric measure (like d4p in ordinary QFT) known beyond a few loops - therefore no definition of higher-loop amplitutes
A measure on supermoduli space indeed exists and can be used to define all-loop amplitudes. The problem is that, except for small genus, it does not appear that the supermoduli spaces are split supermanifolds. Therefore there is no way to split the integration up into an integral over odd coordinates and an integral over even coordinates. The problem with higher-loop amplitudes is then a technical one: there is a definition, but we do not know how to evaluate the expression in closed form.

 - no proof of finiteness of higher-loop amplitutes
For the bosonic string, modular invariance maps the region of geometries where UV divergences would appear to points in moduli space which correspond to IR physics. The bosonic theory has a special IR divergence due to the tachyon. The other potential IR divergences come from special points in moduli space where you have degenerate handles or punctures coming together.

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.

 - no proof of convergence of the perturbation series
It's rarely the case that one expects a perturbation series to converge, rather perturbative series are asymptotic series. Even in ordinary QM, if we consider the harmonic oscillator with a ##\lambda x^4## perturbation, the radius of convergence of the perturbation series is zero.

 Recognitions: Science Advisor 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.

 Quote by Haelfix 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.
Yes, his talk in the previous week in Bonn at the StringMath workshop was about that (improved understanding and construction of super rieman surfaces); I attended both talks. The first talk was more technical than the one in Munich and I found it more interesting. That applies to other some talks in Bonn, as compared to the ones of Strings 2012 as well.

But alas, what sense does it make to discuss this here.

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 Quote by fzero The problem is that, except for small genus, it does not appear that the supermoduli spaces are split supermanifolds. Therefore there is no way to split the integration up into an integral over odd coordinates and an integral over even coordinates. The problem with higher-loop amplitudes is then a technical one: there is a definition, but we do not know how to evaluate the expression in closed form. ... If the supermoduli space is not split, you can't sum over spin structures until you've integrated over the supermoduli.
Thanks for the clarification. Is there a paper to understand the mathematical details of "split and non-split supermanifolds"?

 Quote by fzero It's rarely the case that one expects a perturbation series to converge, rather perturbative series are asymptotic series.
I know. But w/o an explicit calculation for strings it may be hard to guess the behaviour of the series.

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 Quote by tom.stoer Thanks for the clarification. Is there a paper to understand the mathematical details of "split and non-split supermanifolds"?
I've never found a particular reference that I was completely happy with. Googling around now for free things, the lectures at http://www2.mathematik.hu-berlin.de/...10/11:%20Super seem ok and concise. Split supermanifolds are first mentioned in Lecture 4. For some directly relevant comments you might as well also read http://golem.ph.utexas.edu/~distler/...es/000477.html.

 I know. But w/o an explicit calculation for strings it may be hard to guess the behaviour of the series.
Yes, but the issue of whether it blows up at the 6th order or at the 12th is probably not physically relevant.

 Recognitions: Science Advisor 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?
 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.

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 Quote by suprised 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.
Hello S. it's nice to see you back and contributing to our discussions with your distinctive tone of voice!

I just tried the video link for David Gross's "Outlook and Vision" talk
http://www.theorie.physik.uni-muench...oss/index.html
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:
http://www.theorie.physik.uni-muench...012/index.html

Folks might want to watch some of Ooguri's "Conference Summary":
http://www.theorie.physik.uni-muench...uri/index.html
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.

 Quote by tom.stoer 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?
You don't know what Witten is interested in and why. One month ago he wrote a condensed matter theory paper with Shou-Cheng Zhang and Xiao-Liang Qi(http://arxiv.org/abs/1206.1407). It's hard to predict his next move.