Sunday 17 August 2008

Strings ante portas

Tomorrow Strings 2008 kick off here at CERN. The place and the timing of the conference were carefully planned to coincide with the first LHC results that would hint toward string theory. The plan didn't quite work out due to the LHC schedule slip, which means we have to wait one more year for the ultimate confirmation of string theory. The expectation makes it all even more exciting.

The warm-up for Strings 2008 was the Summer Institute on String Phenomenology that has been taking place at CERN TH during the last month. Although I'm usually attracted by wordplay, puns and oxymorons, this time I didn't manage to attend many talks. That's partly due to my summer travelling, and partly due to my summer paresse. Among the few talks I've seen I best remember the one by Cumrun Vafa who talked about F-theory phenomenology. He presented a simple and elegant construction that connects F-theory to reality (that is to the MSSM). Although I wasn't able to grasp all the details, the picture below gives a rough idea:
For detailed experimental predictions, the experimentalists from ATLAS and CMS are encouraged to consult this paper. Although there are no specific predictions for the superparticle spectrum, your perspective may be changed by the fact that the Higgs particle you will discover is in reality a matter curve on Riemann surfaces located at the intersection between the
GUT model seven-brane and additional seven-branes in the full compactification where the U(1) hypercharge flux is non-vanishing. For the neutrino physicists, the important piece of information is that the neutrinos are Dirac or Majorana and their masses are roughly of the order of what is observed. I heard some skeptics saying that back in the old days phenomenology meant a different thing, but such grumbling should not be taken seriously.

Highlights from the conference along with more nasty comments are soon to appear on this blog. Live webcast here or via technically more advanced Lubos' blog.


Anonymous said...

I want tenure so I can make posts like this....

Anonymous said...

Dear Compatriot,
If you really want to see some experimental predictions, then you should look here:
You can see how low string mass can nullify the landscape and anthropic nonsense.

Anonymous said...

Did Vafa mention the paper by Saulina et. al where they took Vafa's setup and constructed a model with gauge-mediated susy breaking arXiv:0808.1571[hep-th]?
It looks like they were able to derive the "Sweet spot SUSY" scenario which is very intriguing. Don't you think?

Jester said...

It is probably interesting from the string-model-building point of view. What I wanted to say is that what matters from the phenomenological point of view is the superparticle spectrum. For that purpose, the field theoretical framework (gauge mediation, in the case you quote) is fully sufficient, and the F-theory approach does not provide any new piece of information.

I don't complain about F-theory model building - I do complain about claiming relevance for phenomenology.

Alejandro Rivero said...

Till now, the most spectacular thing is the display of portables from the audience (to which I contribute my iRex and an Aspire One)

(Also funny, the problems on the speaker side, to project the slides)

Anonymous said...

I agree that gauge mediated SUSY breaking mechanism is captured by a field theoretic approach, no question about it. But there are thousands of models with gauge mediated SUSY breaking with all kinds of adhoc assumptions. The detailed properties of the messenger sector as well as the hidden and visible sectors such as mass scales, allowed and forbidden couplings, etc, cannot be apriory determined just from field theory. In the paper I mentioned, Saulina et al explicitely relied on the F-theory construction to determine some of those properties. So, you cannot just say that there was no new piece of information from F-theory.

Anonymous said...

the susy breaking scale in the F-theory models is arbitrary and not determined by the model. It has to be, it is sourced by an instanton and the amplitude of the instanton comes from the closed string sector whose dynamics are not considered.
the most the paper says is that the amplitude of the instanton can be consistent with having a 1GeV gravitino. which one may say is another kind of adhoc assumption.

Anonymous said...

Sure, the scale of m_{3/2} is not completely determined. However, the form of the superpotential is completely determined by the underlying geometry which, among other things, forbids the generation of the B\mu term and sets the scale of \mu to be that of the SUSY breaking scale as opposed to the GUT scale. The fact that the corresponding geometry gives a SUSY GUT with no exotics and simultaneously addresses other problems such as the doublet-triplet splitting, the supersymmetric CP problem etc. is very non-trivial in my opinion.

Anonymous said...

Certainly the models have something interesting. In particular, the matter content is nice. But let's not get carried away. The gravitino mass is undetermined. The geometry has nothing to do with the susy CP problems (if this is solved here by anything, it is solved by the mediation mechanism - gauge mediation is a field theory mechanism and not an string theory one.) Various fields which are both local and dynamical (e.g. the instanton amplitude) have been frozen. Make them dynamical, and they will give runaway.

Don't get me wrong, it is good that people work on this. But it is also good to be spared claims that suddenly F-theory has solved all open problems in phenomenology (which was the impression I got reading the second long paper, YMMV...)

Alejandro Rivero said...

note the F-saga follows in arXiv:0806.0102 "Experimental Predictions". It is interesting that they "require that any viable model contain precisely three
generations of chiral matter".

Ibañez also adds some other teams (besides UAM, of course) actually having models with three generations:
Donagi, Ovrut, Faraggi,... but to me it seems a bit ad-hoc, to choose Z2 or Z3 to quotient, without further classification theorems to apply.

Honestly, HEP theory does not help very much to select a mechanism for generations. The only hint, told by Faraggi (I believe. Or was it Ovrut?) time ago, is that we need a given number of fermions to hit the meeting of couplings in GUT running. Well, there is also that another hint from mine: the sBootstrap of SU(5) flavour. But it is only group theory (yet).

Another hint I thought last week: if you take seriusly that the yukawa of the top is the only natural one, the other put to zero, then you can consider the limit of infinite mass for W and Z. In this limit, the neutrinos *and the top* decouple, while the gauge group reduces to SU(3)xU(1). But it means that we have a sort of generation-less scenario, and the 24 fermions of the standard model (counting antiparticles, so one 4-component fermion for each yukawa parameter) have reduced to 18.

Jim Eadon said...

Strings has failed spectacularly. Why the bullshit? Return to physics, my degree subject, where experiment rules, not self-denial rubblish. Strings is embarrassing a noble subject.