# Strings 2014

This coming week and the next Princeton will host both the big yearly string theory conference Strings 2014, and Prospects in Theoretical Physics 2014, a program designed to train young physicists in string theory.
Princeton is definitely the right place for this, since it now is very much a singular point in the world-wide theoretical physics research community. At the IAS the director is a string theorist, so is the past director (now faculty member). Of the other four senior HEP theorists, three are string theorists and one might be described as a fellow-traveller. Over at the university, of the nine faculty in HEP theory, all are string theorists except for one junior faculty member.

One will be able to follow the Strings 2014 talks live here, and video and slides should be posted here.

The Strings 20XX conferences provide a good place to see what the latest trends in string theory are, with the talks chosen to highlight what some of the most influential people in the field consider the most interesting work. I’ve written posts on the blog here about previous such conferences, which one can compare to this year’s to see how the field has evolved. Looking at the list of over 70 talks and their topics, some things that strike me (in many cases, much the same things as in other recent years):

• Talks actually about strings are a small minority (20%), something that has been true for quite a few years. The percentage may have grown from a minimum back in 2011 when some of the speakers were mentioning the small role strings were playing at a string theory conference.
• AdS/CFT and holography remain a dominant theme, as they have for many years. Possible applications of this to condensed matter physics are a continuing hot topic. The previous hot topic of this kind, applying AdS/CFT to heavy ion physics, now seems to be dead, something people would rather not talk about anymore since it never worked out as advertised.
• Amplitudes are the other big hot topic.
• Discussion of the LHC and hoped-for LHC results in the past was often a major topic at these conferences. Now that the LHC results are in and a huge disappointment (no SUSY or extra dimensions), it looks like there’s a chance the LHC will not be mentioned at all at this year’s conference, with “string phenomenology” in general the topic of only a very few talks.
• String phenomenology does have its own yearly conference (see here), but at least as far as the US participants go, the top US research institutions are not represented there, whereas they are heavily represented at the Princeton conference. Whatever “string phenomenology” is these days, it’s not popular at all among the Princeton crowd. It’s no longer being done at the most prestigious US institutions, and in Europe is concentrated in certain places (popular in England for some reason, not at all in France).
• While research into string theory unification schemes now seems to be very unpopular at Princeton, for some reason it’s a topic that the young must still be trained in. The PiTP program includes a series of lectures on string compactications, for which the Princeton people needed to bring in Martijn Wijnholt from Munich, one of the places still doing this kind of thing.
• To the extent there’s anything about connection to experiment, B-modes are the hot topic.
• There was a time when mathematicians were sometimes invited to Strings 20XX, but that’s over and done with. It seems most prominent string theorists no longer want to hear anything from mathematicians.
• Finally, zero about the multiverse or the landscape. Clearly some on the organizing committee still have strong opinions and are not going to tolerate that kind of nonsense.
• Witten will just give a 15 min welcoming speech. In the past, David Gross has ended the conference with a “vision” speech. This year there will be five “vision talks”, and it may be interesting to see a wider range of opinions on where the field is heading.

Update: One more notable thing about this version of the yearly conference is that (as far as I can tell), it’s the first one in many years that has not included a promotional public talk about string theory. It may very well be that this was considered unnecessary in Princeton.

Update: Martin Wijnholt’s lectures to the students and postdocs in Princeton about string compactifications are available here. Lots of nice material on Calabi-Yaus and algebraic geometry, nothing at all about extracting the standard model from all this. One thing that has always surprised me is how little most string theorists know about the state of the art of getting particle physics out of the theory. This is less surprising now after seeing the kind of lectures they get on the subject.

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### 44 Responses to Strings 2014

1. Bernhard says:

If Witten himself is not giving a scientific talk, I guess that speaks about the health of the subject.

2. Bob Jones says:

Stringy mathematics is being discussed at a different conference:

http://www.ihes.fr/jsp/site/Portal.jsp?document_id=3481&portlet_id=14

3. layman says:

Bernhard,

Or the fact that he is on the *local* organizing committee and therefore not allowed to speak. This has been the policy forever.

You are embarrassing yourself.

4. Peter Woit says:

Bernhard,
That’s not necessarily true, since Witten is one of the local organizers, and there’s some prejudice towards not having organizers invite themselves to speak (a few of the local organizers will speak, but this may be the only major conference that Arkani-Hamed doesn’t speak at).

Bob Jones,
Not a whole lot of either string theory or physicists at that one…

5. Peter Woit says:

layman,
Since three members of the local organizing committee are speaking, seems to me that it’s you that are embarassing yourself. Of course, since you’re hiding behind anonymity, that’s not a problem for you I guess….

6. piscator says:

Not quite sure why you say string phenomenology is popular in England but not in France – quite a lot of people in the Paris area do some variety of string pheno. There are probably more students in England doing string pheno, but France (for cultural reasons?) has very few PhD students full stop.

7. Peter Woit says:

piscator,
Perhaps you’re right, I may have been over-generalizing from an impression of Oxford vs. IHES. I do think there’s a lot of evidence for a strong US pattern of string phenomenology not being pursued at the highest-ranked institutions, wonder if there’s any similar pattern in Europe. Of if not, why not. England was an example where I could think of string phenomenologists at well-known institutions, France not, but perhaps this is just due to less familiarity with the French system.

8. piscator says:

Peter,

There are a lot of places in Paris so I forget who is exactly where, but an immediate list of names in this area or thereabouts is Bena/Dudas/Goodsell/Grana/Halmagyi, and then there are people like Antoniadis who are there some of the time – I think some of these are at the Grandes Ecoles as well.

Generally I think string phenomenology is much stronger in Europe than the US – in Germany there is the very large Lust group in Munich, and then big groups at Bonn and DESY, in Spain there is Madrid (Ibanez, Uranga, Marchesano)…not sure why there is such a difference to the US, where there is almost a void between people working on BSM x-dimensional models and the mathematical physics side of string theory.

9. Bob Jones says:

What are you smoking, Peter? Almost every single one of those speakers is working on some aspect of mirror symmetry…

10. Navneeth says:

This year there will be five “vision talks”, and it may be interesting to see a wider range of opinions on where the field is heading.

Perhaps Dr. Witten will provide a surprise final talk in which he reveals that all five visions can be considered as different facets of an over-arching M-Vision. 😉

11. Andy says:

“It seems most prominent string theorists no longer want to hear anything from mathematicians.”

It seems you’re unaware of the existence (since 2011) of a conference called String-Math, attracting crowds of the same order of magnitude as (if not higher than) Strings itself.

12. Peter Woit says:

Andy,
I’m well aware of it. Most prominent string theorists go to Strings 20XX, few go to Strings-Math 201X. I think it’s undeniable that most of those on the Strings 20XX organizing committee are less interested in interacting with mathematicians now than they were at many points in the past.

I’m not claiming there is no active field of research involving mathematics and string theory, with many mathematicians participating, just that most US physics departments and most physicists working in string theory have little interest in it (and less than in the past).

13. Andy says:

Peter,

most prominent string theorists go to String-Maths. A quick look at the list of speakers (which is a fortiori strictly included in the list of participants) of SM2012 in Bonn will prove you wrong. I also disagree that “most” people in the organising committee are less interested in the interaction with mathematicians now than in the past. Except perhaps for Verlinde, I think this is precisely false for each and every of them (especially Arkani-Hamed and including Witten – just have a look at his scientific production during the last year)

My considered, possibly misplaced and certainly fully biased opinion is that the StringsMaths interaction has rarely been as active as today: the easiest example to pick is the huge amount work on AGT (“huge” is the right word), which is largely a string-theoretic and/or string-motivated subject, and a top research priority for – my turn to say it now – most prominent senior string theorists (Nekrasov, Gaiotto, Gukov, Moore, Vafa, Witten himself, amidst lots of others): something with few-to-none precedents after the SW paper 20 years ago.

I think – and I’m sure that the two of us will agree on this – this is only good news for the subject.

14. Peter Woit says:

Andy,
The concept of the Strings 20XX conferences has always been to cover all areas where something interesting is happening in string theory, not just areas not covered at other conferences. It’s traditionally not supposed to be a conference specializing in only certain areas. If it has devolved into mainly a specialist conference on AdS/CFT + amplitudes, that’s a phenomenon worth taking notice of.

I looked earlier at the speaker list of Strings-Math 2014 and just took a look at the ones for 2012 and 2013. I disagree that these lists contain a significant fraction of the most prominent string theorists. To quantify the matter, one definition of the most prominent string theorists would be the winners of Milner’s \$3 million award. Zero of these were speaking at the Strings-Math conference last week, four will be speaking at Strings 2014, with three more on the local organizing committee so presumably there but not speaking, and two more (Strominger and Vafa) this year’s runners up for the award. That makes nine versus zero….

15. Peter Woit says:

Andy,
I just noticed that Princeton has a press release out, claiming over 600 participants at Strings 2014. For Strings-Math 2014, looks like about 125. Not sure that’s the same order of magnitude…

Also in the press release: they’re covering the “many strands of modern string theory”. If math is one of them, for some reason mathematicians aren’t part of it.

16. Bob Jones says:

The Strings conference also has mathematical talks (see the ones by Cheng, Kachru, and probably also Cordova, Moore, and Vafa).

17. Peter Woit says:

Bob Jones,
Sure, of the 70-odd talks, some will have material of mathematical interest. My comment was just that mathematicians aren’t the ones being asked to talk about this.

18. Brian Dennehy says:

Apologies for being off-topic but ‘layman’s comment is sadly a reminder that things like meanness to others is not entirely absent in the research community. I can only assume that ‘the health of the subject’ is something that ‘layman’ has become emotionally invested in.

19. Peter Woit says:

Brian,
Researchers (“layman” appears to be one, coming from a major research institution) responding to criticism anonymously with arrogant and mis-informed denunciations of others as being idiots doesn’t really look good, and may very well have something to do with why so few US institutions are willing to hire young string theorists. In my experience, most string theorists are perfectly reasonable people, no more arrogant than your average academic. There are however some unfortunate exceptions, including prominent bloggers and others who like to take advantage of blog comment section anonymity.

20. Jeff M says:

Uh, Peter, hate to be pedantic, but 600 and 125 are the same order of magnitude (2, to be exact). 🙂

21. Peter Woit says:

I dunno Jeff, maybe it’s the physicist in me, but I’d say 600 is the same order of magnitude as 1000, and 125 is the same order of magnitude as 100, so….

22. Chris Herzog says:

I often like your posts Peter, but this one came across as a bit too knee jerk for my taste.
1) AdS/QCD is not dead but has maybe left the purview of formal string theory. To name one success, the idea of measuring viscosity with respect entropy density has left a lasting impact on the heavy-ion community.
2) I agree with Andy 100% that the strings/math connection is alive and well everywhere, from Korea to the U.S. to Europe. The fact that mathematicians are not speaking at Strings I view as an accident. Who knows? Perhaps the mathematicians read your blog and decided to turn the organizers down…
3) The absence of string phenomenologists at top US research institutions is in my mind an indication that US institutions may no longer be as top in theory as they used to be, compared with the rest of the world. We continue to train the world’s finest for the moment, but many of them now choose (or are forced) to go elsewhere for jobs.

23. Peter Woit says:

Hi Chris,

I agree that strings/math is alive and well (although, as in physics, the strings are often disappearing, and we’re really talking about qft/math). Would be interesting to know if the conference organizers invited mathematicians, I still suspect not, that the overlap with math is something that physicists in general have drawn back from (which is too bad).

My own take on the absence of hiring at top US institutions of people working on models for getting the SM out of string theory is that the best theorists, string theorists and otherwise, have for a while now realized this is an idea that doesn’t work, or at least one that is going nowhere until someone comes up with some very different idea. The dozen or more string theory faculty at Princeton are the best in the business and they’re still hiring in the area, but not “string phenomenologists”. I’m not aware of them trying to hire such a person and failing because they lost out to another institution. What I don’t understand is why this is still so popular in Europe.

As for AdS/QCD, maybe my comment about the death of the application to heavy ions was a bit over the top, influenced by some over the top claims about the successes of that subject that were common in the past.

Glad to hear you often enjoy the posts, despite some disagreements…

24. piscator says:

A European perspective on this is that string theory faculty at Princeton are just not the best in the business anymore, unless the business’ is defined as the uber-narrow area of mathematical physics inspired by string theory. Whereas the Strings conference has a theoretical mandate to cover the whole of the subject, in practice there has been a narrow focus on topics popular at Princeton.

Most of the talks at Strings – this year as at previous year – are only tangentially related to what physics’ historically means. If you never work on any kind of phenomenology, and your advisor never worked on any kind of phenomenology, you are not going to know very much about it. Most physicists really doesn’t think six-d N=(2,0) theory is an interesting problem to be thinking about.

A slightly broader perspective on this is that each generation, there are certain tools and abilities required to really advance the subject. Physics for 30 years after the second world war was not so mathematical. This created a ripe environment for the fusion of mathematical and physical ability so exemplified by Witten (and others of that generation) to be perfect for making great leaps forward. It’s very unclear that this style of work now is what is really needed.

25. Pneno says:

In fact there are many strong groups working on string phenomenology in the US.
To name a few : Harvard ( L. Anderson (Heterotic and more) , Heckman, Vafa (who have done very important work on F-theory Unification),
Princeton (H. Verlinde; Maldacena and Klebanov on string cosmology; Witten on axions); The Penn group (M. Cvetic, B. Ovrut, Donagi);
Stanford (Silverstein leading work on string cosmology; also Kachru, Kallosh and others); Wisconsin (G. Shiu; L. Evertett); Santa Cruz (M.Dine);
Mc Allister (Cornell); Many others on different aspects of compactifications like D.Morrison, Taylor, Wecht, Halverson; Many other well known physicists work part time on string phenomenology aspects ( S. Dimopoulos (axiverse),
L. Randall (e.g. flavour physics from F-theory), N. Arkani-Hamed (landscape), R. Bousso (landscape), S. Raby (heterotic models), P. Langacker, M. Gaillard, and a very long etc.

26. Chris Herzog says:

Pneno.

A very interesting list. To clarify, I really meant a relative absence. My position is simply that more faculty lines should be devoted to string phenomenology in the US.

27. chris says:

“the idea of measuring viscosity with respect entropy density has left a lasting impact on the heavy-ion community.”

sorry, but i have to strongly disagree with this. there was some interest a few years back, but not much lasting impact i would say. if there is a distant field with a strong influence on heavy ions it is probably cosmology at the moment. the cmb/fireball comparison is much more taked about at the moment than any ads/cft result.

28. Peter Woit says:

piscator,
As I keep pointing out, little of what the many string theorists in Princeton are doing has much to do with mathematics, it seems they chose no mathematicians to speak at the Princeton conference, and few of the many talks there have much to do with mathematics. If you don’t like the current Princeton vision of “string theory”, I don’t think it’s fair to blame it on “mathematics”.

Pneno,
There is some interest in “string cosmology” at top US institutions, especially Stanford, but I think comparing your list to the Strings 2014 speaker list makes my point. Only Anderson, Bousso and Vafa are speakers, with Anderson the only one speaking about phenomenology. And she’s now at Virginia Tech, not Harvard.

29. Peter Shor says:

What people seem to be arguing about is whether the pre-eminent conference in strings is being run by a small group of famous string theorists who have dismissed phenomenology, mathematics, and the LHC, or whether the predominant sentiment in the field as a whole is to dismiss phenomenology, mathematics, and the LHC.

I don’t know which of these alternatives I find more disturbing.

30. Elbi Gilgen says:

It puzzles me that anyone could think that amplitudes are “hot”. Look at the arxiv. In particular, the “Amplituhedron” is deader than any doornail has a right to be.

31. David Meltzer says:

Elbi,
The amplitudehedron work by Nima is probably the most mathematically sophisticated work on amplitudes there is. Probably the only people working on it are Nima, Trnka and maybe a few of his other students. It’s not surprising if it appears dead right now just because so few people are working on it. The amplitudes program is much larger though and a few names I could recommend looking at the papers by Lance Dixon, Zvi Bern, and David Kosower, they really got the subject started and were awarded the Sakurai prize for their work.

Theres a lot of other names I could list but my best recommendation would be to look at one of the amplitudes conferences for more details.

32. Jesper says:

Peter – I just noticed that you posted this comment in “Strings 2XXX”. I wonder if this choice of label is a show of optimism – or pessimism? You could also have chosen Strings XXXX, Strings XXXXX, or – in what I think would be in the optimistic end of your spectrum – Strings 20XX.

33. Peter Woit says:

Jesper,
Yes, extrapolating from the last twenty years, I think there will be a Strings 2100 conference. Might not even be that different than the current ones. I’m much less sure of Strings 3000, but who knows….

34. Shantanu says:

Peter somewhat OT to this thread but not blog
The talks of the recent dark matter conference at CFA are online and in
Lisa Randall’s talk
she is mentioned that supersymmetric models were in trouble even before LHC started
and none of them obey occam’s razor

35. Bernhard says:

Pneno,

Since you seem to know well about string phenomenology, I wonder how much do you believe of real phenomenology the work you mention on your list contains. What I have in mind are realistic string theory models that can connect with experiment. The obvious names that come to mind are Lisa Randall and Arkani-Hamed with extra dimension models, but I think it is fair to say whatever realistic models they built they were more “string inspired” than actual stringy models.

My comment has a direct connection with Peter’s comment about “how little most string theorists know about the state of the art of getting particle physics out of the theory”. Perhaps it doesn’t apply to this list of prominent people, but still, even for them, I have a very hard time finding work that could be directly meaningful to an experimentalist, and at some point this should be the goal of phenomenology, wouldn’t you agree?

36. Pneno says:

Look, Bernhard. Writing a phenomenological model which can be tested at the LHC or other experiment is trivial. Add a few extra
dimensions here and there; extra vector-like particles or non-perturbative stuff; etc. But that is not what we want.
We want to learn what lies beyond the SM and understand the involved principles within a fundamental
theory, and, lets face it, the only serious candidate for that is string theory. Thus we want to learn how string theory might contain
(or not) something resemblingg the SM at low energies. This we have to do taking into account both experimental information
and mathematical consistency, and both are very constraining. This is a tough job since string theory is technically demanding and one also has to
have the physical intuition of what phenomenological problems can and may be addressed. These include
issues like the structure of fermion masses, strong CP problem, SUSY breaking, hierarchy problem, cosmology….
This may take time but some of us prefer that than producing random BSM models which are testable by an experimentalist NOW.
String theory already provided answers to those questions in much firmer grounds than previous BSM traditional model building.
And much more will come, while our knowledge on
compactifications accumulate. In addition string theory has been the source of many of recent ideas physics BSM. I certainly reccomend
the young phenomenologists to learn string theory compactifications if they want to be sufficiently prepared for doing BSM physics
in the future. GUT’s and SUSY are no longer enough.

37. Peter Woit says:

Pneno,
From your description, string phenomenologists have given up on being able to do anything relevant to LHC-scale physics, although they have the capability of generating “random BSM models” if they want to (but you seem to realize that isn’t a very meaningful activity). The same argument applies to VLHC or any other conceivable HEP physics experiment, so you’ve given up on the conventional idea that a better theory is supposed to predict something different and distinctive that can be tested.

You seem to indicate that what is worthwhile to do now is to just try and get the SM out of a sufficiently complex string theory model. There seems to be no evidence that such things are so tightly constrained that you can’t get the SM, so there is no way for anyone to ever show that what you are doing is wrong. But if you “succeed”, get a string model that gives the SM, what have you accomplished other than embedding a relatively simple model in something much more complicated? How will you ever know that what such a complicated creation has anything to do with the real world?

38. akame says:

Peter,
“But if you “succeed”, get a string model that gives the SM, what have you accomplished other than embedding a relatively simple model in something much more complicated? How will you ever know that what such a complicated creation has anything to do with the real world?”,

such a theory would describe particle physics as we know it, and also be a consistent theory of quantum gravity. The embedding of SM into string theory solves the problem of quantum gravity, is that not a worthwhile thing? And if it describes both gravity and particle physics, doesn’t it per definition have a lot to do with the real world? At the very least, it is some “effective theory of everything”, which in itself is no small feat. You can’t reject a theory because “it seems too complicated”. Of course, a simpler model is preferable, but then there needs to be such an alternative.

39. Peter Woit says:

akame,
First of all, arguing that this is a consistent theory of quantum gravity is rather dubious since you don’t know what the theory is (remember, “what is string theory” is still an unanswered question).
But, even giving you that, I still don’t believe that replacing a simple model by an incredibly complicated, completely untestable one is progress in any sense, no matter what your argument is that your untestable model has some better formal property.

40. akame says:

Peter, such a model would be in principle testable, but maybe not at accessible energy scales. Moreover, it is not obvious to me that the theory would be all that much more complicated than the standard model. Even the SM requires us to fix a particular gauge group, a particular particle content, a Higgs sector, there is some weird mechanism for neutrino-masses, 3 generations, there must be something there to explain dark matter, maybe some axion, presumably there also needs to be something new out there other than the Higgs and so on. Maybe all this seems simple because you are used to it, but it really isn’t all that simple. My hope is that an embedding into string theory, maybe using F-theory, could have a similar amount of complexity, just phrased in a very different language, i.e. pick a CY, have some fluxes, place some branes/some elliptic fibration, maybe some O-planes, and get a reasonable model. The amount of data needed could be comparable to the amount you actually need for a non-stringy model of particle physics. And again, a model being “complicated” is not a valid criticism. Physics is about describing nature, you can’t and shouldn’t necessarily require models to be “simple”, whatever that term even means.

41. Peter Woit says:

akame,
In the kind of modeling you’re talking about, as far as I can see, all you’re doing is putting together mathematical components (Calabi-Yaus, elliptic fibrations, etc.) that are much more complicated than the components of the SM (simple Lie groups and their simplest finite-dim representations), according to a conjectural set-up in which you expect to be able to map the complicated structures to the simpler ones of the SM. As far as I can tell, no one has been able to turn this set-up into one that allows you to reliably extract the SM parameters (couplings, mixing angles, Yukawas) as a function of the inputs, except perhaps in special unphysical limiting cases.

This kind of set-up has zero predictive value, because much more is going into it than is coming out. The hallmark of a theory with predictive power is that you put something simple in and get non-trivial complex, testable physical predictions out. Here you’re doing the reverse, having to provide more complex inputs than the physical predictions you are getting out. Yes, you can “model” all sorts of physics this way, but you can’t predict anything, and you’re not doing science in any conventional understanding of the term. Some people think you’re doing mathematics, but I’d disagree with that too.

Yes, you can hope that a miracle will happen, and some particular choice of inputs will provide the complexity of the real world. People have been doing this now for 30 years with no success at all (this idea looks much less promising now than it did in 1985). Hoping for a miracle is just wishful thinking, not science.

42. Nick M. says:

Peter,

The link that you have given to Martin Wijnholt’s lecture at Princeton about “String Compactification” (in the second “Update”) seems to have gotten broken. I “think” the correct (current) links are “ Wijnholt notes UPDATED” and “Lecture 1 slides” and “Lecture 2 slides“. Only trying to be of help.

43. Nick M. says:

Sorry Peter, but I forgot to mention that there is also a third set of slides for the third lecture; “Lecture 3 slides“.

44. Peter Woit says:

Thanks Nick,