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Diary of a Ghost Hunter Vol. 5 by Scott M.

post from The Debris Field on 24 July 2008 02:00:00 AM. © The Debris Field

Diary of a Ghost Hunter Vol. 5 by Scott M. ? family, reviews, health | Gather

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vol-5-by-scott-m.html

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Lattice 2008, Day six

post from Life on the lattice on 24 July 2008 12:57:00 AM. © Life on the lattice

Saturday was the last day of the conference. The first plenary, chaired by Andreas Kronfeld, was devoted to the quest for new physics. Luca Silvestrini spoke about the observed discrepancies between lattice and experiment: A 4.4σ difference in the CP asymmetries in B to K π decays, a 3.8σ difference in f_{D_s}, and a 3σ difference in the phase of the B_s to J/ψ φ decay. Although the LHC is expected to give access to the low-lying part of the particle spectrum of the expected new physics, a Super-B factory will be needed to map the new physics out in detail (the MSSM has 160 parameters). Lattice QCD determinations of quantities of interest at the <1% accuracy level will be needed for these purposes.

Then George Fleming spoke about strong interactions beyond the Standard Model, where technicolor is making a comeback, since only some QCD-like versions of it have been ruled out. The interest in this area centers on "walking" theories with a very slowly running coupling. For SU(3), it is believed that there is a "conformal window" of N_f, where the coupling runs to an IR fixed point in the infrared. Simulations using unrooted staggered fermions to simulate N_f=4,8,12,16 indicate that this window lies somewhere around N_f=12.

The last plenary had Michael Teper speaking about Large-N QCD using old-fashioned OHP slides. N=&infinity; QCD is a theoretical laboratory for ideas about QCD, both because it turns out that as far as the N-dependence of observables is concerned, N=3 is close to N=&infinity;, and because at N=&infinity;, quenched QCD is full QCD, because fermion loops are infinitely suppressed by their colour factors; also, resonances become infinitely narrow as N goes towards infinity, allowing accurate measurements of e.g. the ρ mass, which turn out to be quite close to the real world at N=&infinity;.

This was followed by Hermann Krebs's talk about nuclear effective theories on the lattice. The lattice as a regulator is of course not unique to gauge theories, and nuclear theorists are now performing simulations of effective theories of pions and nucleons to determine the properties of light nuclei and nuclear matter from first principles. The low-energy constants can be either fitted to experiment by giving up an a number of predictions, or can be taken from lattice QCD (once they are determined accurately enough) for a truly first-principles treatment of nuclear physics.

After the end of the session, there was an announcement of the Les Houches Summer School on Lattice QCD in 2009. Then Kostas Orginos thanked the support staff and volunteers, before handing over to the representative of the Lattice 2009 organising committee, who thanked Kostas and his team. Everybody got their well-deserved applause, and then the lattice community was invited to come to Beijing for the Lattice 2009 conference, which is to be held July 26-31, 2009. It was also announced that Lattice 2010 will be held at a yet-to-be-determined location in Europe. And then the conference was over, and everybody said their goodbyes before leaving.

Since my flight only left the next day, I took the opportunity to visit the "Colonial Williamsburg" open-air museum, which I liked a lot better than the Jamestown one, largely because the colonials/locals just went quietly about their business without too much show or spectacle, which I thought gave one a much better impression of what life in the American colonies might have been like.

My flight back went fine, but I didn't get to post the last two summaries earlier.

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http://latticeqcd.blogspot.com/2008/07/lattice-2008-day-six.html

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Lattice 2008, Day five

post from Life on the lattice on 24 July 2008 12:56:00 AM. © Life on the lattice

Friday's first plenary started with a summary talk on heavy-flavour physics on the lattice given by Elvira Gamiz. The most striking point there is what is now being called the "f_{D_s} puzzle", i.e. the difference between lattice predictions (241(3) MeV [HPQCD N_f=2+1], 249(11) MeV [FNAL/MILC N_f=2+1], 244(4)(11) MeV [ETMC N_f=2 preliminary], 251(6)(?) [Alpha N_f=2 preliminary]) and experimental measurements (268(8)(4) MeV [CLEO-c, most recent]) of the D_s meson decay constant, for which new physics is being invoked as an explanation by many. Other topics were semileptonic decays of heavy mesons, which are quite hard to study on the lattice, and B-Bbar mixing parameters, where some also raise the possibility of new physics to explain discrepancies between theory and experiment that have recently arisen.

The next talk was Laurent Lellouch speaking about Kaon physics, and comparing the usefulness SU(2) and SU(3) chiral perturbation theory.

The second plenary session was started by Rob Pisarski speaking about heavy-ion collisions ar RHIC, where the study of the strongly interaction quark-gluon plasma (if it may be called that, since it does not really appear to be the state of matter formerly imagined under the name of quark-gluon plasma) requires methods from non-equilibrium thermodynamics and non-ideal hydrodynamics. One of the long-standing puzzles that appear to be experimental signatures of the QCD phase transition is the suppression of J/ψ final states and jets. Some explanation for these phenomena in terms of the "elliptic flow" of the quark-gluon plasma seems to have been found, but it appears to me that a fundamental undestanding of what is going on in these highly out-of-equilibrium situations involving strongly interacting matter is still a fair way off.

The next talk was related to this topic, as Harvey Meyer spoke about the extraction of hydrodynamical transport coefficients from the spectral functions of correlators of energy-momentum tensors, which requires some clever tricks to get the continuous spectral functions from the correlators measured only at a few discrete points.

After this, Yoshinobu Kuramashi gave a talk about PACS-CS's simulations of N_f=2+1 QCD at and near the physical pion mass. They were thus able to test the applicability of SU(2) and SU(3) chiral perturbation theory, and my interpretation of their results was that both might not be sufficiently well-behaved to be truly valid even at the physical point.

The last talk of the session was given by Tomoteru Yoshie, who gave an introduction and status update on the International Lattice Data Grid (ILDG), which now contains 183 ensembles with a total of 193,000 configurations using 41 Terabyte of storage space.

In the afternoon, there were again parallel sessions, including one in which Rainer Sommer spoke about our group's recent work on the Generalised Eigenvalue Problem for correlator matrices and how to use it in the most efficient manner to get ground and excited state masses and matrix elements, both in QCD and in effective theories such as HQET, and another on in which I talked about a preliminary analysis of D_s physics on the large and fine CLS lattices. Rainer's talk was certainly very well received, and since the potential criticisms of the work that I presented were easy to anticipate, I would say that my talk also went quite well.

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http://latticeqcd.blogspot.com/2008/07/lattice-2008-day-five.html

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Atlas Bear Claims

post from Cryptomundo.com on 24 July 2008 12:09:29 AM. © Cryptomundo.com

In a dialogue between a German and a Frenchman, some clarifications about the Atlas bear are shared with Cryptomundo. Images.

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http://www.cryptomundo.com/cryptozoo-news/atlas-bear/

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Further Adventures of the Garden Yeti

Design Toscano's Bigfoot, the Garden Yeti, is in the news again. With an update on the one stolen from Niki's Quick Six too. Image.

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http://www.cryptomundo.com/cryptozoo-news/pescovitz-yeti/

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