Wednesday, July 16, 2008

Lattice 2008, Day two

Today was a long day, so this will be a short summary. Any typos and inaccuracies in content are to be blamed exclusively on the wine served during the poster session.

After another continental breakfast, the first plenary session of the daym chaired by John Negele, started with a talk by Marc Vanderhaegen about nucleon structure studies. This was this year's experimental talk, for which reason I find myself too ignorant to give a good summary of it; there were lots of plots of experimental results of observables such as the ratio of the electric to magnetic form factors of the proton (which appears to be quite different if measured by unpolarised or by polarised probes for reasons to do with two-photon exchanges), the generalised parton distributions of the nucleon, and the magnetic dipole moment of the Δ(1232) resonance (which is apparently very hard to measure, because the Δ decays strongly and hence is far too short-lived to measure its magnetic moment by the precession method that can be used for stable or quasi-stable particles).

Next was James Zanotti who gave an overview of the work that has been done on hadronic structure from the side of lattice QCD. Again there were lots of plots of the same quantities, this side from lattice simulations, but I have to freely admit that I am way too ignorant of hadronic structure studies to appreciate this work very well. A better summary of the progress in this area that might be given in the comments would be appreciated.

After the coffee break, the second plenary session of the morning continued with Martin Savage in the chair. The nuclear thread of the previous session was continued by Silas Beane speaking about Hadronic interactions and nuclear physics. This was probably the funniest talk I have ever heard at a lattice conference (it included inter alia a picture of a crying baby held by G.W. Bush, illustrating the exponential growth with time of noise in baryonic channels, and of a live rabbit being pulled from a top hat). Multi-hadron states are now being targetted by lattice simulations, but dealing with the noise will require petascale computing.

The final plenary talk of the day was by Colin Morningstar, who talked about studies of excited hadronic states. His talk concentrated almost exclusively on the very extensive work done in this area by his collaborators, who have indeed made some remarkable progress on this very difficult problem; however, there are also some other approaches to extracting information on excited states, which may well turn out to not be competitive with the variational method, but might still deserve a mention at least in this blog.

After lunch with some colleagues, taken at an Asian buffet place that was both better and much more reasonably priced than the university canteen, I attended parallel sessions. The more remarkable talks included Constantia Alexandrou presenting a new method to extract excited states, which seemed to work remarkably well given that it appeared to be largely a rather glorified form of uniform random search. Progress towards using the HISQ action for simulations with staggered quarks including dynamical charm was presented by Alexei Bazavov. Michael Clark spoke about adaptive multi-grid methods for QCD as potential competitors to deflation methods. A presentation an a new high-performance computing architecture was given by John Mucci, the CEO of SiCortex, the company producing it -- it sounded a bit like marketing, but if their computers really only use 200 W per 100 GFlops and can run with ordinary air-cooling that would be quite amazing.

Finally, the poster session closed the day. My poster on the determination of the O(Nfαsa2) improvement coefficients for the Lüscher-Weisz action with dynamical HISQ fermions appeared to be received quite well by its intended audience. The food was gone quickly, and the wine not much more slowly. By an amusing coincidence there was a poster from another group about pretty much exactly the same work as I am doing with people at Zeuthen at the moment.

1 comment:

T Burch said...

These summaries are really nice. It's really interesting to see someone else's perspective of the conference and the field in general.

Your comments concerning the excited hadron plenary are rather forgiving. Not only were other methods ignored, but also a wealth of work performed by other groups (some of them collaborators of the speaker) with similar methods. A quick survey of the current abstracts or an invitation email to the community would surely have uncovered more.

Speaking of which, we were as surprised as you to see others working on the same stuff as that presented in C Hagen's poster. Rainer Sommer's talk was encouraging for us in that we are seemingly on the right track with excited-state couplings and heavy-light kinetic corrections.