Fri·Sep 2, 2005Friday·September 2, 2005

1. 01*

   Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential

   M. Doring🇩🇪 · S. Ejiri🇯🇵 · O. Kaczmarek🇩🇪 · F. Karsch🇩🇪 · E. Laermann🇩🇪

   We analyze the dependence of heavy quark free energies on the baryon chemical potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the chemical potential which circumvents the sign problem. The Taylor expansion coefficients of colour singlet and colour averaged free energies are calculated and from this the expansion coefficients for the corresponding screening masses are determined. We find that for small mu_b the free energies of a static quark anti-quark pair decrease in a medium with a net excess of quarks and that screening is well described by a screening mass which increases with increasing mu_b. The mu_b-dependent corrections to the screening masses are well described by perturbation theory for T > 2 T_c. In particular, we find for all temperatures above T_c that the expansion coefficients for singlet and colour averaged screening masses differ by a factor 2.

   hep-lathep-phnucl-thEPJC(2006)·51 citations
2. 02*

   Determining the low energy parameters of Wilson Chiral Perturbation Theory

   Sinya Aoki🇯🇵 · Oliver Bar🇯🇵

   We report preliminary results of a Wilson Chiral Perturbation Theory (WChPT) analysis of twisted mass lattice QCD data. The quenched data, previously published by two different groups, was generated with two definitions for the critical quark mass and shows a strong non-linear quark mass dependence for small quark masses for the pion mass definition (``bending phenomenon''). We find that WChPT describes this characteristic curvature fairly well. Fits to the data provide estimates for combinations of low-energy parameters, even though the errors are sizable.

   hep-latPoS(2006)·13 citations
3. 03*

   Lattice calculation of low energy constants with Ginsparg-Wilson type fermions

   Christof Gattringer🇦🇹 · Philipp Huber🇦🇹 · C. B. Lang🇦🇹

   We present a quenched lattice calculation of low energy constants using the chirally improved Dirac operator. Several lattice sizes at different lattice spacings are studied. We systematically compare various methods for computing these quantities, using pseudoscalar and axial vector correlators. We find consistent results for the different approaches, giving rise to f_\pi = 96(2)(4) MeV, f_K = 106(1)(8) MeV, f_K/f_\pi=1.11(1)(2), Sigma= -(286(4)(31) MeV)^3, the average light quark mass m = 4.1(2.4) MeV and m_s = 101(8) MeV.

   hep-latPRD(2005)·24 citations
4. 04*

   Implementing Hybrid Monte Carlo with stout-smeared chirally improved Dirac operators

   C. B. Lang🇦🇹 · Pushan Majumdar🇦🇹 · Wolfgang Ortner🇦🇹

   We discuss our implementation of dynamical Ginsparg-Wilson type fermions using a stout-smeared chirally improved Dirac operator. Such operators have been studied extensively in quenched calculations within the Bern-Graz-Regensburg (BGR) collaboration. Here we discuss the development and testing of the Hybrid Monte Carlo algorithm with this Dirac operator. We study the chiral properties of this operator in a dynamical setup, comparing, e.g., the spectra of the operator for the dynamical and quenched cases. We then discuss quantitative features of the algorithm like autocorrelation and performance.

   hep-latPoS(2006)·6 citations
5. 05*

   First results from dynamical chirally improved fermions

   C. B.Lang🇦🇹 · Pushan Majumdar🇦🇹 · Wolfgang Ortner🇦🇹

   We simulate Quantum Chromodynamics in four Euclidean dimensions with two (degenerate mass) flavors of dynamical quarks. The Dirac operator is the so-called chirally improved operator that has been studied so far in quenched calculations. We now present results of an implementation with the Hybrid Monte Carlo (HMC) algorithm including stout smearing. Our results are from an 8^3x16 lattice with tadpole improved Luescher-Weisz gauge action. We present our estimate of the lattice spacing, the pi and rho meson masses and evidence for tunneling between different topological sectors.

   hep-latPoS(2006)·9 citations
6. 06*

   Studying glueball masses in non-Abelian LGT with the LW algorithm

   Marco Panero🇮🇪

   We address a study of glueball masses in the confining regime of SU(2) in D=3 using an algorithm inspired by the multi-level scheme. Our method, which exploits the locality of the action to achieve high precision results, is based on a technique already used for compact QED, and generalises it to the non-Abelian case. We discuss the main features of this method, in comparison with other algorithms that have been used in similar studies.

   hep-lathep-phhep-thPoS(2006)·0 citations
7. 07*

   Contour-improved versus fixed-order perturbation theory in hadronic tau decays

   Matthias Jamin🇪🇸

   The hadronic decay rate of the tau lepton serves as one of the most precise determinations of the QCD coupling alpha_s. The dominant theoretical source of uncertainty at present resides in the seeming disparity of two approaches to improving the perturbative expansion with the help of the renormalisation group, namely fixed-order and contour-improved perturbation theory. In this work it is demonstrated that in fact both approaches yield compatible results. However, the fixed-order series is found to oscillate around the contour-improved result with an oscillation frequency of approximately six perturbative orders, approaching it until about the 30th order, after which the expansion reveals its asymptotic nature. Additionally, the renormalisation scale and scheme dependencies of the perturbative series for the tau hadronic width are investigated in detail.

   ↳ hep-phhep-latJHEP(2005)·54 citations
8. 08*

   The Universe from Scratch

   R. Loll🇳🇱 · J. Ambjorn🇩🇰 · J. Jurkiewicz🇵🇱

   A fascinating and deep question about nature is what one would see if one could probe space and time at smaller and smaller distances. Already the 19th-century founders of modern geometry contemplated the possibility that a piece of empty space that looks completely smooth and structureless to the naked eye might have an intricate microstructure at a much smaller scale. Our vastly increased understanding of the physical world acquired during the 20th century has made this a certainty. The laws of quantum theory tell us that looking at spacetime at ever smaller scales requires ever larger energies, and, according to Einstein's theory of general relativity, this will alter spacetime itself: it will acquire structure in the form of "curvature". What we still lack is a definitive Theory of Quantum Gravity to give us a detailed and quantitative description of the highly curved and quantum-fluctuating geometry of spacetime at this so-called Planck scale. - This article outlines a particular approach to constructing such a theory, that of Causal Dynamical Triangulations, and its achievements so far in deriving from first principles why spacetime is what it is, from the tiniest realms of the quantum to the large-scale structure of the universe.

   ↳ hep-thgr-qchep-latContemp.Phys.(2006)·122 citations
9. 09*

   A General Theory of Goodness of Fit in Likelihood Fits

   Rajendran Raja🇺🇸

   Maximum likelihood fits to data can be performed using binned data and unbinned data. The likelihood fits in either case produce only the fitted quantities but not the goodness of fit. With binned data, one can obtain a measure of the goodness of fit by using the ${\chi }^2$ method, after the maximum likelihood fitting is performed. With unbinned data, currently, the fitted parameters are obtained but no measure of goodness of fit is available. This remains, to date, an unsolved problem in statistics. By considering the transformation properties of likelihood functions with respect to change of variable, we conclude that the likelihood ratio of the theoretically predicted probability density to that of {\it the data density} is invariant under change of variable and provides the goodness of fit. We show how to apply this likelihood ratio for binned as well as unbinned likelihoods and show that even the ${\chi }^2$ test is a special case of this general theory. In order to calculate errors in the fitted quantities, we need to solve the problem of inverse probabilities. We use Bayes' theorem to do this, using the data density obtained in the goodness of fit. This permits one to invert the probabilities without the use of a Bayesian prior. The resulting statistics is consistent with frequentist ideas.

   ↳ physics.data-anhep-exhep-lat7 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.