## Tuesday, June 15, 2010

### David Gross: Theoretical visions

David Gross's talks have been linked or embedded into The Reference Frame many times.

But what can you do about it - he's just a favorite speaking physicist of mine - not only because I agree with 99+ percent of his opinions about fundamental and particle physics. ;-)

At a recent Physics at the LHC 2010 conference in Hamburg (the conferences began in 2003 in Prague and continued in Vienna 04, Cracow 06, and Split 08), he gave this 42-minute talk:
Theoretical visions (video)
He considers the LHC as the greatest technical achievement of mankind - our generations' answer to the pyramids.

Gross shows how the collider began to produce data. For example, in 2010, it reproduced the 1964 discovery of Omega minus. Fourty-six years ago, one event was enough to find it and no automatization was used in its analysis.

These days, people can't even understand that one event may be enough and that this kind of physics may be done without computers.

David Gross seems to be confident about his knowledge of the LHC events. So he's showing chaotic pictures of the trajectories, making you feel that he can really see it is a Z-boson or a W-boson. ;-)

At 7:00, he turns his attention to the theory which has been doing well since 1964. The Standard Theory - which is David's proposed new name for the Standard Model - is so successful that it's been deeply frustrating both for experimenters and theorists.

The SM is not complete because of various reasons. Experimentally, it is because of: dark matter; neutrino masses (easily added); baryon asymmetry; cosmic acceleration (the C.C.). Theoretically, it is because of: the lack of unification; the hierarchy problem; unexplained subtleties of the matter sector - number of generations, masses, mixing; cosmology, inflation, vacuum energy not incorporated.

In 1993, Gross gave a talk a the Lepton and Photon conference. At that time, the SSC was being built and it was approaching its death, too. Gross gave ten predictions about the HEP experiments between 1993 and 2008:
1. Yes: top-quark will be old news: indeed, 173 GeV
2. No: this prediction about epsilon'/epsilon measured nonzero (new CP-violation) was wrong because the 40 TeV SSC died - instead of running since 1999; only a hole in Texas remained
3. No: for the same reason: David predicted the observation of at least two light Higgses by 1998; the failure of the prediction is not his fault
4. No: convincing evidence for SUSY particles: not yet, to say the least
5. Yes, mostly: Omega=1 will be measured within 10%; some components were listed; however, David incorrectly assumed the C.C. (dark energy) to be zero
6. Yes: MSW mechanism would be established as a solution of the solar neutrino problem
7. Weak yes: evidence for quark-gluon plasma is here; but David thought of a weakly interacting, perturbative one
8. No: new Z-mesons
9. No: cloudy evidence for superstrings available by 1999
10. Yes: there will be a real surprise; indeed, there has been one, the nonzero C.C.
Ten more predictions for the theory were discussed.
1. Yes: lattice QCD will achieve 1% precision
2. No: analytic QCD will derive the Regge behavior etc. in the small "x" regime
3. Yes: an expansion of QCD, gauge theories etc. in 1/N will be developed: indeed, David approximately predicted the AdS/CFT revolution
4. No: cosmological origin of baryons understood; the necessary components are known but we can't calculate the results - all details unknown
5. Yes: understanding of density fluctuations; it worked nicely
6. No: string field theory will be useful, especially to clarify the symmetry structure of string theory; it wasn't - it turned out to be pure formalism to rephrase the same, mostly perturbative knowledge in a different way
7. Yes: specific low-energy models of SUSY breaking would be found; they have surely been found although it's unclear which one is right if any
8. Yes, preliminary: conceptual revolution shedding light on non-perturbative string dynamics and the emergence of spacetime; it's on its way
9. Yes: fate of evaporating black holes will be understood without modifications of QM; that surely worked nicely to him
10. No, no: we will understand why the C.C. is zero; well, it's not zero and we don't understand why it is what it is, anyway ;-)
I agree that he did pretty well - 50% score is good enough for these rather specific statements. His new 2010-2020 predictions say
1. QCD tests will include NLO, NNLO, and fragmentation and hadronization will be incorporated into the improved QCD calculations
2. ATLAS and CMS will find Higgs candidate
3. There will be convincing evidence for SUSY - just like your humble correspondent, he believes that SUSY is more likely than not
4. Linear collider construction plans will be underway - in CERN (see more information about their CLIC project); America will join the European Center of Nuclear Research ;-)
5. Direct detection of dark matter wind will have taken place
6. ATLAS will see a crossover to the perturbative quark-gluon plasma
7. Some new Z-bosons will be discovered
8. Gravitational waves and B-modes will be observed
9. String theory will begin to produce predictions
10. We will have an explanation why the C.C. is small: again :-)
I am not sure about the U.S. becoming another European country (it's 50:50 for me), I am not sure about the progress about the C.C. (also 50:50) and I would bet that new Z-bosons are somewhat "less likely than yes" but otherwise I share these predictions.
By the way, a few hours ago, The Register and BBC did a very good job in explaining the muon-antimuon anomalous difference measured by D0 at the Fermilab a month ago. Just like your humble correspondent did, Paul Rincon says that if the signal is real, the most sensible explanation is a collection of five God particles instead of just one Higgs, a multiplication predicted by MSSM, e.g. in the "uplifted supersymmetry" region promoted in a preprint by Dobrescu, Fox, and Martin.
David Gross enjoyed the conference because no one said the words "anthropic principle". David smashed the arrogant theorists who boast that the questions that they can't answer can't be answered. ;-)

In 1937, Dirac discussed the "large number problem", the existence of very high (or very small) dimensionless ratios in Nature. As a great physicist, he avoided the anthropic arguments even though he could. Instead, he has proposed to link all the large numbers to one of them - the size of the Universe in atomic units (a figure that keeps on increasing) by various mechanisms. His theory predicted the cosmological evolution of the constants and has been ruled out.

Dirac's particular "large number problem" - about the "M_{Planck}/M_{Proton}" ratio - has been solved by Gross and friends. It's due to asymptotic freedom. The strong coupling runs logarithmically, so from a sensible value such as 1/25 at the Planck scale, it inevitably reaches the value g=1 at an exponentially lower scale - and this is where the masses of the hadrons inevitably sit.

This success gives David (and me) the belief that an analogous success may explain the tiny C.C., too. Gross mentions that the C.C. is "just" 64 orders of magnitude below the order-of-magnitude predictions from SUSY. The C.C. is the quartic power of a mass, so the mass scale itself is just 16 orders of magnitudes off. We did better with the QCD, not a huge problem! ;-)

We've done it before. We just need more hints. The fun is just beginning.

And that's David's memo.