What Are the Current Trends in String Theory Research?

[marcus]

Each year, the annual String conference provides us with a kind of snapshot of the field as it is today. The lineup of invited speakers and the titles of their talks give an idea of the current activity and interests of string researchers.

This year Strings 2012 is in Munich and starts on Monday 23 July. The organizers plan to have 45 talks. As of today titles of 16 of the 45 are listed.

F. Alday Mixed correlators in N=4 SYM
T. Dimofte Building blocks in 3d SCFT
M. Gaberdiel Minimal Model Holography
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
A. Karch Recent Applications of the Gauge/Gravity Correspondence to QCD and Condensed Matter Physics
S. Kortner Status and latest results of the LHC
H. Nicolai Alternative approaches to quantum gravity: a brief survey
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
S. Raju Scattering Amplitudes and AdS/CFT Correlators
J. Schwarz Opening Lecture
A. Strominger Progress in dS/CFT
A. Uranga Update on string phenomenology
E. Witten Superstring Perturbation Theory Revisited
M. Yamazaki Networks, Quivers and 3-manifolds
X. Yin Higher Spin Holography

Overall attendance figures for some past conferences. In several cases (e.g. Madrid) a cap was placed on attendance and registration was only allowed up to a certain limit:

Registered participants in the annual conference (some years omitted for brevity)

Strings 2003 Kyoto     396
Strings 2005 Toronto   415
Strings 2007 Madrid    440
Strings 2009 Rome      450
Strings 2011 Uppsala   265
Strings 2012 Munich    384 (prelim.)

So far 384 people have registered to attend the conference, of which roughly half are listed as "student", "graduate student", "PhD student", or "postdoc."

The state of the field is also reflected in what kinds of theorists physics departments are most interested in hiring: e.g. which particle theory specializations (cosmology, phenomenology, string, lattice...) currently figure most prominently. The particle theory job picture for this year (Usa + Canada, first-time faculty positions) is the same as it was 8 June, over a month ago. Twelve HEP theorists have offers, of whom one is a string theorist. Faculty hiring for the fall semester could still change but now seems approximately complete for the year.

Annual first time faculty hires in theoretical particle physics (Usa + Canada)
(Up through 2010, the rates are averaged over 3 years intervals.)

period          1999-2001   2002-2004   2005-2007   2008-2010  2011   2012
HEP theory hires   18         24          23          13        11     12
string hires        9          8           6           2         1      1

The source used for the preliminary 2012 estimates: http://particle.physics.ucdavis.edu/rumor/doku.php
Source for previous years: http://www.physics.utoronto.ca/~poppitz/Jobs94-08

 

[Mark M]

Great job putting this together. Of the talks currently listed, the two that look most interesting to me are Strominger's talk on dS/CFT, and Uranga's talk on string phenomenology.

 

[marcus]

Thanks! I tend to agree with you. Phenomenology is the key area, a kind of information bottleneck, and any development there would be highly significant. Also Strominger (I have a high regard for him) often gives one of the more interesting talks at the annual conference. In this case the restriction to AdS has been a major handicap for something like 10 years. Given the apparent positive cosmo constant they in some sense HAVE to break out of the AdS trap. So (IMHO as nonexpert observer) everybody is going to be interested by what he presents.

Here is the website's speaker list with titles posted so far:
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/talks.html
We can check back periodically with this link to see how it shapes up as more talk titles are added.

I also find it interesting that Hermann Nicolai (another of my favorite string people) is giving a survey talk on non-string QG alternatives. The organizers apparently thought this topic would interest those attending the conference.

 

[Mark M]

I wonder if Strominger will make any mention of the result of Hawking/Hartle/Hertog. That is, the paper in which they attempted to show that a negative cosmological constant would result in a positive acceleration of expansion.

Another talk that looks interesting is the one that will be given by Kortner regarding the latest results at LHC.

 

[marcus]

I wonder if Strominger will make any mention of the result of Hawking/Hartle/Hertog. That is, the paper in which they attempted to show that a negative cosmological constant would result in a positive acceleration of expansion.

Another talk that looks interesting is the one that will be given by Kortner regarding the latest results at LHC.

I think he almost has to make some reference to that paper---the authors are so prominent.
You're right about the Kortner talk, it's likely to be well worth watching!

I'll do an update on the conference while I'm at it. About a week to go. Registration is at 384, half are listed as grad student, postdoc and the like.
As of today titles of 24 of the 45 planned talks are listed. The strongest common theme appears to be CFT-based holography, i.e. gauge/gravity correspondence and its applications. To show thematic emphasis I've highlighted the CFT/holo talks:

M. Aganagic Knots, Mirror Symmetry and Large N Duality
F. Alday Mixed correlators in N=4 SYM
M. Cvetič Non-perturbative Effects in F-theory Compactifications
T. Dimofte Building blocks in 3d SCFT
M. Gaberdiel Minimal Model Holography
D. Gross Outlook/Vision
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
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
S. Kortner Status and latest results of the LHC
H. Nicolai Alternative approaches to quantum gravity: a brief survey
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
H. Ooguri Conference Summary
E. Rabinovici (In) Stabilities and complementarity in AdS/CFT
S. Raju Scattering Amplitudes and AdS/CFT Correlators
O. Schlotterer Hidden simplicity in superstring amplitudes
J. Schwarz Opening Lecture
A. Strominger Progress in dS/CFT
A. Uranga Update on string phenomenology
C. Vafa Topological Strings and Their Diverse Applications
E. Witten Superstring Perturbation Theory Revisited
M. Yamazaki Networks, Quivers and 3-manifolds
X. Yin Higher Spin Holography

Strings 2013 will be held in Seoul, June 24-28.

 

[Mark M]

Great job again with the update.

D. Gross Outlook/Vision

I'm curious about what he'll have to say, considering the lackluster performance of string theory over the past few years.

 

[tom.stoer]

Have a look at these slides from "string 2007" and "strings 2009":

http://strings2009.roma2.infn.it/talks/Gross_Strings09.pdf, slide #16
http://www.ift.uam.es/strings07/040_scientific07_contents/transparences/gross.pdf , slide#22

where Gross asked some interesting questions - on which he probably is still waiting for reply:

WHAT IS STRING THEORY?
This is a strange question since we clearly know what string theory is to the extent that we can construct the theory and calculate some of its properties. However our construction of the theory has proceeded in an ad hoc fashion, often producing, for apparently mysterious reasons, structures that appear miraculous. It is evident that we are far from fully understanding the deep symmetries and physical principles that must underlie these theories. It is hoped that the recent efforts to construct covariant second quantized string field theories will shed light on this crucial question.

We still do not understand what string theory is.
We do not have a formulation of the dynamical principle behind ST. All we have is a vast array of dual formulations, most of which are defined by methods for constructing consistent semiclassical (perturbative) expansions about a given background (classical solution).

What is the fundamental formulation of string theory?

WHAT IS MISSING ?
Perhaps “String theory” is like quantum field theory - a framework and not a definitive theory.
Perhaps we are missing a fundamentally new principle of symmetry, of dynamics, of consistency, ... that leads to a unique solution --- not a “vacuum” but a space-time, a cosmology.
Emergent Space-Time

 

[member 11137]

I think he almost has to make some reference to that paper---the authors are so prominent.
You're right about the Kortner talk, it's likely to be well worth watching!

I'll do an update on the conference while I'm at it. About a week to go. Registration is at 384, half are listed as grad student, postdoc and the like.
As of today titles of 24 of the 45 planned talks are listed. The strongest common theme appears to be CFT-based holography, i.e. gauge/gravity correspondence and its applications. To show thematic emphasis I've highlighted the CFT/holo talks:

M. Aganagic Knots, Mirror Symmetry and Large N Duality
F. Alday Mixed correlators in N=4 SYM
M. Cvetič Non-perturbative Effects in F-theory Compactifications
T. Dimofte Building blocks in 3d SCFT
M. Gaberdiel Minimal Model Holography
D. Gross Outlook/Vision
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
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
S. Kortner Status and latest results of the LHC
H. Nicolai Alternative approaches to quantum gravity: a brief survey
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
H. Ooguri Conference Summary
E. Rabinovici (In) Stabilities and complementarity in AdS/CFT
S. Raju Scattering Amplitudes and AdS/CFT Correlators
O. Schlotterer Hidden simplicity in superstring amplitudes
J. Schwarz Opening Lecture
A. Strominger Progress in dS/CFT
A. Uranga Update on string phenomenology
C. Vafa Topological Strings and Their Diverse Applications
E. Witten Superstring Perturbation Theory Revisited
M. Yamazaki Networks, Quivers and 3-manifolds
X. Yin Higher Spin Holography

Strings 2013 will be held in Seoul, June 24-28.

Unfortunately, I have no holydays next week... I would have appreciate to ear some of the conferences. My preference goes to G. Horowitz. Do you know if outsider like me can get abstracts from a part of the conferences?

 

[marcus]

Unfortunately, I have no holydays next week... I would have appreciate to ear some of the conferences. My preference goes to G. Horowitz. Do you know if outsider like me can get abstracts from a part of the conferences?

I hope and expect that video of all the talks will eventually be freely accessible online.
This is how it was last year when the Strings 2011 conference was held at Uppsala Sweden.

I'll do an update on the conference while I'm at it. Next year's Strings will be held in Seoul, June 24-28, 2013. Strings 2012 starts Monday 23 July. Registration at 384, about half being grad student, postdoc and the like. A prevalent topic appears to be CFT-based holography so I've highlighted the CFT/holo talks. As of today, titles of 28 of the 45 planned talks are listed.:

M. Aganagic Knots, Mirror Symmetry and Large N Duality
F. Alday Mixed correlators in N=4 SYM
J. Carrasco Generic multiloop methods for gauge and gravity scattering amplitudes, a guided tour with pedagogic aspiration
A. Castro Path integrals in 3D gravity
M. Cvetič Non-perturbative Effects in F-theory Compactifications
T. Dimofte Building blocks in 3d SCFT
M. Gaberdiel Minimal Model Holography
D. Gross Outlook/Vision
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
S. Kachru New Horizons in Finite Density Field Theory and String Theory
A. Karch Recent Applications of the Gauge/Gravity Correspondence to QCD and Condensed Matter Physics
S. Kortner Status and latest results of the LHC
H. Nicolai Alternative approaches to quantum gravity: a brief survey
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
H. Ooguri Conference Summary
A. Polyakov Quantum Instability of the de Sitter space
E. Rabinovici (In) Stabilities and complementarity in AdS/CFT
S. Raju Scattering Amplitudes and AdS/CFT Correlators
O. Schlotterer Hidden simplicity in superstring amplitudes
J. Schwarz Opening Lecture
A. Strominger Progress in dS/CFT
A. Uranga Update on string phenomenology
C. Vafa Topological Strings and Their Diverse Applications
E. Witten Superstring Perturbation Theory Revisited
M. Yamazaki Networks, Quivers and 3-manifolds
X. Yin Higher Spin Holography
B. Zwiebach Glimpses of Double Field Theory Geometry

I was intrigued by the title of Polyakov's talk: Quantum Instability of the de Sitter space
I cannot find a recent Polyakov paper about this. But, since he recently wrote a paper string-modeling AdS space
http://arxiv.org/abs/1106.1558
A String Model for AdS Gravity and Higher Spins,
I speculate that he tried to do something similar for dS space and found it didn't work. Hence a kind of negative result.

 

[atyy]

The Newton Institute had a 6 month long programme http://www.Newton.ac.uk/programmes/BSM/index.html

Many of its seminars online, which provides another view of current string concerns.
http://www.Newton.ac.uk/programmes/BSM/bsmw05p.html
http://www.Newton.ac.uk/programmes/BSM/seminars/

Lu Ran's http://www.Newton.ac.uk/programmes/BSM/seminars/062716451.html incorporates consideration of some evidence for a gamma-ray line from dark matter annihilation in Fermi LAT's data.

 

[w4k4b4lool4]

I wonder if Strominger will make any mention of the result of Hawking/Hartle/Hertog. That is, the paper in which they attempted to show that a negative cosmological constant would result in a positive acceleration of expansion.

yes, that's an interesting paper .. you should have been at the Brussels conference a few weeks ago, where all three, namely Hartle, Hawking, Hertog, and also Strominger, Susskind, ..., among others were present:
http://www.solvayinstitutes.be/events/cosmology2012/cosmology.html
Hartle presented the paper you are referring to. Strominger's dS/CFT talk was a bit more vague.

The above statistics make me sad by the way ...

But thanks Marcus for gathering all this interesting info in one place!

Wakabaloola

 

[marcus]

You are very welcome Waka! And I am concerned that some stats sadden you.
I am sad myself about what appears to me to be too many gradstudents and postdocs in the pipeline. There is definitely demand but there is an oversupply I think. This is just my hunch since I am very far from having direct knowledge.
There are also (I think) valid research problems to work on, but with an oversupply of people there could be a fair amount of duplication.
I worry mainly about the gradstudents and postdocs, not the established people.

On a more cheerful note, if you are the flexible creative person you seem to be from a few of your posts (with subtlety and a sense of humor as well I would think) then prospects can't really be so bad. You must be primarily worried about other people. I shouldn't be so foolish as to make a wild guess like that based on superficial first-impression appearances, but there it is.

I think if I was in your shoes (as I imagine or guess the situation) I would talk to Hermann Nicolai. that might be a vacuous suggestion: you may know him and already have gotten his ideas. I think he understands the borderland areas around String and to some extent the whole map of QG. One should be prepared to be mobile and cross boundaries, not be too much limited by formalities and conventional approaches.

At the Max Born symposium in 2009, Nicolai talked a bit about some work of Shaposhnikov---he seems to me to be another "amphibian". http://www.ift.uni.wroc.pl/~planckscale/

I think the list of Strings 2012 talks is now complete. I should post a link and hope that people study the list, and think about it. Do you have any comment on the major themes that seem to be emerging? Anything new?

You mentioned Asymptotic Safety. I'm interested by that too. I'm trying to understand better how the world might look from your perspective as a string theorist with some acquaintance with bordering fields such as Loop, Asymptotic Safety, probably applied AdS/CFT and doubtless much more.

I almost forgot, cosmology. It is the testing ground for all these approaches: String, Loop, Asym. Safety, and surely several more. I think if I were young (not a retired person just watching) I would try to learn all the active approaches that bear on understanding the start of expansion and the background radiation, inflation, etc etc. Understand the "big bang/bounce" from every possible avenue and viewpoint. Try to see how to distinguish by observational testing.

 

[marcus]

The program of Strings 2012 is complete! Here is the list of talks:
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/talks.html

Let's hope there are many interesting ones and that they become available as online video, or at least as slides PDF.

I'd like very much to get other people's comment on the lineup of talks and the predominant topics.
Maybe I should paste it in:

M. Aganagic Knots, Mirror Symmetry and Large N Duality
F. Alday Mixed correlators in N=4 SYM
L. Anderson New Aspects of Heterotic Geometry and Phenomenology
I. Antoniadis Aspects of string phenomenology in the new LHC era
N. Arkani-Hamed Scattering Amplitudes and the Positive Grassmannian
C. Bachas AdS4/CFT3 and Gravity Localization
F. Cachazo Gravity in Twistor Space
J. Carrasco Generic multiloop methods for gauge and gravity scattering amplitudes, a guided tour with pedagogic aspiration
A. Castro Path integrals in 3D gravity
M. Cvetič Non-perturbative Effects in F-theory Compactifications
T. Dimofte Class R: A User's Guide
S. Dimopoulos What has the LHC done to Theory?
B. Freivogel Predictions from Eternal Inflation
M. Gaberdiel Minimal Model Holography
D. Gaiotto Domain walls and RG flows
C. Gomez Black holes as graviton condensates at the critical point of a quantum phase transition
D. Gross Outlook and Vision
J. Heckman Covariant Non-Commutative Geometry From String Theory
G. Horowitz Why General Relativity is like a High Temperature Superconductor
N. Iqbal Friedel oscillations and horizon charge in 1D holographic liquids
S. Kachru New Horizons in Finite Density Field Theory and String Theory
A. Karch Recent Applications of the Gauge/Gravity Correspondence to QCD and Condensed Matter Physics
Z. Komargodski Comments on the Renormalization Group and Diverse Applications
S. Kortner Status and latest results of the LHC
C. Kounnas Non-singular Superstring Cosmologies
J. Maldacena Constraining theories with higher spin symmetry
H. Nicolai Alternative approaches to quantum gravity: a brief survey
H.P. Nilles Heterotic supersymmetry: the legacy of D=10 and N=4
H. Ooguri Conference Summary
A. Polyakov Quantum Instability of the de Sitter space
E. Rabinovici (In) Stabilities and complementarity in AdS/CFT
L. Rastelli Bootstrapping the Superconformal Index
O. Schlotterer Hidden simplicity in superstring amplitudes
J. Schwarz Opening Lecture (I)
N. Seiberg Chern-Simons Contact Terms
E. Silverstein RG and unitarity in spacetime-dependent QFT
A. Strominger Progress in dS/CFT
A. Uranga Update on string phenomenology
C. Vafa Topological Strings and Their Diverse Applications
G. Veneziano Opening Lecture (II)
E. Witten Superstring Perturbation Theory Revisited
M. Yamazaki Networks, Quivers and 3-manifolds
X. Yin Higher Spin Holography
B. Zwiebach Glimpses of Double Field Theory Geometry

 

[marcus]

*speakers giving hour talks ("survey talks"). others have 30 minutes
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/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

 

[marcus]

All these eight people's slides PDF (or powerpoint in some cases) are now posted online.
I've looked at Strominger's and thought it was interesting. Would have liked an audio with it explaining some of the diagrams and cartoons:

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

Also looked at Horowitz and Kachru's slides. All nice presentations. Seem to be basically about finding apps for AdS/CFT. See also Karch survey talk. (applications of gauge/gravity). Probably applied holography is the main topic for Monday.
Strominger's talk somehow bolder more ambitious---opens up wide horizon of unanswered questions about deSitter space, see the end of his talk. Just some preliminary impressions of mine. To get a better idea you should check it and some other talks out.

*Karch gave the hour talk ("overview talk") today. The other's had 30-minute slots.

 

[tom.stoer]

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?

 

[marcus]

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?

That's a fascinating question!
Could you take a copy of the list in post #13 (or post #14) above
and put a star* or @ symbol beside each talk that is about a physical issue?
We could separate them out. Looking at the two lists might stimulate insights
I would very much like to see a rough division like that!

 

[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

 

[marcus]

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.

 

[marcus]

Videos are now available for the Monday talks.
http://www.theorie.physik.uni-muenchen.de/videos/strings2012/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

 

[marcus]

Videos are now available for the Monday and Tuesday talks.
http://www.theorie.physik.uni-muenchen.de/videos/strings2012/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/strings/strings2012/strings_files/program/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.)
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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?
===

 

[Mark M]

Thanks for posting these Marcus! I'm going to start watching them now.

 

[marcus]

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."
https://www.amazon.com/dp/0521517524/?tag=pfamazon01-20
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.

 

[tom.stoer]

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

Did he address something?

What else?

Would be nice to see your comments

 

[marcus]

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/strings/strings2012/strings_files/program/Talks/Tuesday/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.

 

[fzero]

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.

 

[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.

 

[suprised]

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.

 

[tom.stoer]

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"?

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.

 

[fzero]

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/~groegerj/teaching_YO!_en.html#WS10/11:%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/blog/archives/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.

 

[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?

 

[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 don't you keep on going.

 

[marcus]

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 don't 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-muenchen.de/videos/strings2012/gross/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-muenchen.de/videos/strings2012/index.html

Folks might want to watch some of Ooguri's "Conference Summary":
http://www.theorie.physik.uni-muenchen.de/videos/strings2012/ooguri/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.

 

[lfighter]

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.

 

[marcus]

The Churchill speech that Ooguri starts paraphrasing at (or slightly before) minute 18 was given in June 1940 before the House of Commons. It was one of his finest and contained this passage:

"We shall go on to the end. We shall fight in France, we shall fight on the seas and oceans, we shall fight with growing confidence and growing strength in the air, we shall defend our island, whatever the cost may be. We shall fight on the beaches, we shall fight on the landing grounds, we shall fight in the fields and in the streets, we shall fight in the hills; we shall never surrender,..."

http://en.wikipedia.org/wiki/We_shall_fight_on_the_beaches

It was interesting that Ooguri thought necessary to use some of his time discussing the DEMOGRAPHICS of the string program: median age and national makeup of conference participants. He had prepared some bar-graphs and statistics.
=======================

It helps, I think, to make a clear distinction between the String program (consisting of people of a range of professional standing and interests, at various institutions) and String as a published body of theory.

Suprised used the word "decline". Of course the String program can decline (in terms of how much current research is cited, or in terms of new faculty hiring, or some other observable index) but this does not mean the body of theory declines. On the contrary, the body of published theory can only grow as more and more papers accumulate.

I suppose there could be questions of direction, or how focused current work is on the real problems of cosmology and the target areas that Tom mentioned. Direction focus and realness are somehow quality issues and our assessments tend to be subjective.