## Monday, August 18, 2008 ... //

### Strings 2008: Monday

...and live broadcast

Click the picture above for the Strings 2008 website. Click here for a separate window with the live webcast.

On September 10th, the video above also broadcasts the live webcast, "The First Large Hadron Collider beam", since 9:00 am Prague=CERN Summer Time (midnight Californian daylight saving time).

Monday morning

At Strings 2008, some officials gave nice introductions in the morning. It was announced that 1 octant of the LHC is already testing a beam (probably 81 whose chart says "hot" now: everything is at 1.9 K, however). String theory was also presented as a tool to achieve peace - which was also the reason why they established CERN itself. ;-) Funny.

Gabriele Veneziano spoke about high-energy string scattering that played an important role when he initiated string theory (at CERN) exactly 40 years ago. However, he focused on some newer work on the scalings. Although I view these topics interesting, I found the talk a bit boring, full of too many "small points", and I think it is wrong that the discipline and time schedule was not demanded by the organizers.

Andy Strominger was caught in a cute debate about e-mail with a female colleague before he began his talk. ;-) In 2 seconds, he - a Windows guy - learned to walk forward and backward (with a Mac). He prepared a talk about chiral 3D gravity that we have discussed two weeks ago.

He nicely motivated his talk by saying that string theory is the only consistent quantum framework complex enough to contain black holes but it would be better to have simpler toy models for some purposes. He said that 3D gravity may look trivial (Einstein's equation = flatness) but it actually had (BTZ in AdS) black holes so there could be something. But is there a full theory?

Andy was implicitly skeptical about Witten's monstrous work and added the chiral term and explained physics of the theory, carefully looking at the asymptotic isometry group - the quotient of the allowed and trivial diffeomorphisms. The theory becomes chiral at the critical vacuum energy. The holomorphic factorization, assumed (but probably incorrect) in Witten's monstrous case, becomes a consistency requirement.

Finally, he connected the work with observations - namely those of extremal 4D Kerr black holes: everything must move counter-clockwise around the horizon which is analogous to the chirality in the 3D case. He manages to properly reproduce the "S=2.pi.J" entropy of these black holes. He finally conjectures that a black hole in the telescope is dual to a c=2e46 CFT or something like that. Excellent talk!

Jeff asked about monster symmetry of Andy's CFT. Andy interpreted Davide's paper as making it impossible to have monster symmetry reps above the k=1 level. But in 4D, the monster group could be there.

Renata Kallosh updated her 2007 talk on string cosmology. She began with the WMAP5 successes and with the proposed stringy models of inflation with gravity waves. LambdaCDM is not going to go away: physicists should "adapt" to it. ;-) She advocated the landscape description of these things and encouraged people to develop "as many models as possible" so that they can fit the future data - a formulation I find amusing: if you cover a parameter space by models, it doesn't mean that the model that happens to coincide with the observed parameter is the right model (a truism that the anthropic people could disagree with).

The B-modes could be observed soon (or the bound moved by a lot), she says. A racetrack model of hers predicts no cosmic strings and no gravity waves. Silverstein's work deriving gravity waves from monodromies was described. There's been a lot of experimental charts in the data. 10% of cosmic strings with n=1 (exactly) works as well as 0% of cosmic strings with n<1.

She described a general problem of their favorite models predicting observable gravity waves: natural models typically predict very heavy gravitinos, with masses above the inflationary Hubble scale. My conclusion would be, of course, that it is fair to say that they predict that gravity waves won't be seen.

That ends the main part of her talk. But she mentioned a few words about her involvement in the finiteness of N=8 supergravity. She will publish a preprint tomorrow about this idea. Her proposal is to link the counterterms in the 4+32 covariant superspace with those in the 4+16 light-cone superspace, using the helicity variables. She claims that she has proved the perturbative finiteness (the counterterms would break Lorentz symmetry in the light cone gauge) assuming the absence of BRST anomalies in N=8 SUGRA (i.e. that it's possible to express N=8 SUGRA, whatever it is, both covariantly and in the light cone gauge equivalently). Very interesting.

Alexander Polyakov, the father of many things including the Polyakov action, prepared a talk on global warming. ;-) Well, global warming of de Sitter space. The global warming fad has gotten very far: a string theory conference. The talk began with a global dimming of the video. He continued with tired mountaineers :-) and after 5 minutes, I have still no idea what the talk will be about. After 6 minutes, he finally mentioned an interesting question I care about - how does highly-curved AdS/CFT gravity becomes a free gauge theory. But he won't be talking about it.

Instead, the talk is about the de Sitter space but I still don't know what exactly it will be about. Something about particle production in it. But what? Fine, after 15 minutes, he said he wants to refine the Bunch-Davies propagator. He requires the eternity condition (in-vacuum = out-vacuum). Spider (pure creation) diagrams vanish (no particle production proving instability). After 20 minutes, he said he is just beginning his talk. ;-)

He asked whether this stability (cancellation) is possible in other FRW geometries. Has it something to do with the Huygens principle (different in even and odd D's)? I don't know. ;-) At this moment, it's clear that the talk is about the de Sitter stability. The title is explained by a nonzero probability for the temperature to grow at each point of de Sitter space. I missed where it came from. 2 minutes after the normal end of the talk, Polyakov was talking about two squirrels watching a gymnast. ;-) Great Gentleman, very chaotic talk.

Hirosi Ooguri asked how he wants to analytically continue the coupling and adjust it at the same moment. I didn't understand the answer. Andy Strominger asked something and the answer was not known. Juan Maldacena asked in which formalism the Bunch-Davies vacuum was claimed to be unstable. I think that Polyakov avoided the direct answer but he probably thinks that it is unstable in all approaches.

Monday afternoon

This half-day is dedicated to talks about the LHC, the collider scheduled to run a mere 500 meters (ATLAS) from the conference hall (Main Auditorium) on September 10th.

Lyn Evans, CERN's manager, begins with a description of the status of the LHC machine. Casually dressed, he announced all the octants to be at 1.9 K - even though the picture shows a hot 81 sector now (because of a beam?). Geography of the sectors - mostly independent "factories" - is explained. There's a lot of pre-acceleration. The LEP infrastructure was re-used to reduce the price of the LHC by 50%.

The 1.9 K temperature is below the cosmic microwave background and it is the coldest place in the Universe unless some aliens are ahead of us in particle physics. ;-) Funny music begins to play. String theorists are then explained how to create a perfect dipole field (Rob Myers doesn't have to listen now). 1.9 K was chosen for the helium to be as heat-conductive as possible. A non-trivial transition from 1.9 K to 4 K is needed: superconductors can't support temperature gradients. High-Tc superconductors are helpful.

Cooling and warming is fast enough now for a problem to cost 3 months of interruption. He showed and explained the temperature charts of the sectors. Now, when the sectors are cool, they are commissioning the hardware. Hundreds of circuits and 1,600 power supplies must be tested individually. Global tests of arcs will follow. Beam commissioning worked instantly on 8/08/08, when the Olympics and the South Ossetia war began. Champagne. Things look great, many inverse femtobarns will be collected in 2009.

Question: What is training of magnets? Another question: PS (Proton Synchrotron, *1959) is the oldest thing and it will collapse, like all old things, what will you do? Evans: It works well but in a few years, it may be renovated.

Jos Engelen spoke about detectors that are also ready. They have to sustain higher energies, luminosities, and speed than their ancestors. Size is increased. Every 25 nanoseconds, there's a beam (in fact, with 1,000 tracks) hitting you. Fast materials and many pixels are needed. Like the rapping Alpinekat, he explains what LHCb, ALICE, ATLAS, and CMS will be doing. Also, TOTEM will look at the total cross section, LHCf for something else, and a place will look for magnetic monopoles.

He talks about the resolution of muon energy and missing transverse energy. The detectors should be affordable, he thought when he was young. ;-) Multiple scattering has to be avoided (light thin material). No cracks! Muon spectrometers work differently at CMS and ATLAS (the biggest difference between the two) - tracking mostly inside or outside, respectively. A lot of details about calorimetry etc. It's impressive but overwhelming. ATLAS is a ship in the bottle. ;-) The LHC is not quite horizontal: extra mechanical support for the detector is needed. CMS is more compact than ATLAS (that's the "C") but modular.

In 2008, CMS and friends are ready for the 10 inverse picobarns and to re-discover the Standard Model. ;-) ALICE will track heavy ions - lower luminosity, higher multiplicity. Some of the detectors are not in the full 4.pi directions. In LHCb, everything is just 1/2 of a full detector, for money reasons. The grid is a reality, 100,000 processors will deal with 15 terabytes a year. The Higgs and SUSY may come in 2009. Question about upgrades: multiplying the luminosity by 10 will require new detector centers. Question about energy upgrades: up to 10% can work for free. Question: what was the best and worst decision? The best was that Lyn became the boss and the worst decision - he can now answer what it is. ;-) Question: whose triggers are better? They're different. ATLAS used classical, level 1,2,3 triggers while CMS chose a technology that didn't yet exist at the time.

Oliver Buchmüller talks about new physics at the LHC. His talk has three parts: the challenging LHC environment; the Standard Model rediscovery; and CMS and ATLAS scenarios to see new particles. Hard environment: new high energy makes old things look new, cross sections can be very low and very high. He already showed ready abstracts of papers announcing discoveries of new charged particles at sqrt(s)=10 TeV. ;-)

But in 2008, they must start with rediscovering of the Standard Model (maybe including the top quark), a pillar for new discoveries. When will those occur? Either early or late, the historical data show. ;-) The light Higgs (115-120 GeV), favored by Tevatron, will take a long time to be discovered. Peskin said that once the Higgs will be seen, it will no longer be interesting (because other new physics will already have been found). LHC may become a huge SUSY factory quickly - by 2009 - but only if the detector behavior and backgrounds are well understood.

He explained a point misunderstood by some theorists. "SUSY search" doesn't mean that they're dogmatically believing a particular theoretical model. It means a class of events - signatures - in this case a lot of missing energy plus a lot of leptons (from a cascade decay of a heavy new particle): so the "SUSY search" can stand for many other types of models, too. Also, the Higgs is wanted, dead or alive. Bounty: USD 5,000 and probably USD 10 billion because finding it is enough to make the LHC worth it, he thinks. For the mass below 200 GeV, the peak is very small and we may wait until 2010-2011. Exotic new physics at 1-3 TeV sometimes...

Question on black holes: they could be seen in 2009 if they exist. Question: smoking gun for SUSY (and not something else)? Hard to determine the spins directly etc.

The talks from other days are available in separate articles:
Tuesday, Wednesday, Thursday, Friday

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