Results From The UKQCD Parallel Tempering Project

We present results from our study of the Parallel Tempering algorithm. We examine the swapping acceptance rate of a twin subensemble PT system. We use action matching technology in an attempt to maximise the swap acceptance rate. We model the autocorrelation times within Parallel Tempering ensembles in terms of autocorrelation times from Hybrid Monte Carlo. We present estimates for the autocorrelation times of the plaquette operator.Comment: LATTICE98(algorithms

Continuing Progress on a Lattice QCD Software Infrastructure

We report on the progress of the software effort in the QCD Application Area of SciDAC. In particular, we discuss how the software developed under SciDAC enabled the aggressive exploitation of leadership computers, and we report on progress in the area of QCD software for multi-core architectures.Comment: 5 Pages, to appear in the Proceedings of SciDAC 2008 conference, (Seattle, July 13-17, 2008), Conference Poster Presentation Proceeding

Exploratory spectrum calculations using overlap valence quarks on a staggered sea

We present exploratory results for the hadron mass spectrum and pseudoscalar meson decay constants using mixed actions. We use improved staggered sea quarks and HYP-smeared overlap valence quarks. We obtain good signals on 10 configurations at one lattice spacing and two different sets of sea quark masses.Comment: Lattice2004(spectrum), 3pages, 4 figure

Neural-network analysis of Parton Distribution Functions from Ioffe-time pseudodistributions

International audienceWe extract two nonsinglet nucleon Parton Distribution Functions from lattice QCD data for reduced Ioffe-time pseudodistributions. We perform such analysis within the NNPDF framework, considering data coming from different lattice ensembles and dis- cussing in detail the treatment of the different source of systematics involved in the fit. We introduce a recipe for taking care of systematics and use it to perform our extraction of light-cone PDFs

Nucleon, Δ\Delta and Ω\Omega excited states in Nf=2+1N_f=2+1 lattice QCD

The energies of the excited states of the Nucleon, $\Delta$ and $\Omega$ are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculation is performed at three values of the light quark mass, corresponding to pion masses $m_{\pi}$ = 392(4), 438(3) and 521(3) MeV. We employ the variational method with a large basis of interpolating operators enabling six energies in each irreducible representation of the lattice to be distinguished clearly. We compare our calculation with the low-lying experimental spectrum, with which we find reasonable agreement in the pattern of states. The need to include operators that couple to the expected multi-hadron states in the spectrum is clearly identified.Comment: Revised for publication. References added, Table VI expanded to add strange baryon multiparticle thresholds and multiparticle thresholds added to Figs. 4, 5 and 6. 15 pages, 6 figure

The nucleon mass in N_f=2 lattice QCD: finite size effects from chiral perturbation theory

In the framework of relativistic SU(2)_f baryon chiral perturbation theory we calculate the volume dependence of the nucleon mass up to and including O(p^4). Since the parameters in the resulting finite size formulae are fixed from the pion mass dependence of the large volume nucleon masses and from phenomenology, we obtain a parameter-free prediction of the finite size effects. We present mass data from the recent N_f=2 simulations of the UKQCD and QCDSF collaborations and compare these data as well as published mass values from the dynamical simulations of the CP-PACS and JLQCD collaborations with the theoretical expectations. Remarkable agreement between the lattice data and the predictions of chiral perturbation theory in a finite volume is found.Comment: 23 pages, 5 figures; references added + minor corrections; one more reference added, typo in eq.(25) corrected, additional clarifying remark

Lattice QCD with mixed actions

We discuss some of the implications of simulating QCD when the action used for the sea quarks is different from that used for the valence quarks. We present exploratory results for the hadron mass spectrum and pseudoscalar meson decay constants using improved staggered sea quarks and HYP-smeared overlap valence quarks. We propose a method for matching the valence quark mass to the sea quark mass and demonstrate it on UKQCD clover data in the simpler case where the sea and valence actions are the same.Comment: 15 pages, 10 figures some minor modification to text and figures. Accepted for publicatio

Present Constraints on the H-dibaryon at the Physical Point from Lattice QCD

The current constraints from lattice QCD on the existence of the H-dibaryon are discussed. With only two significant lattice QCD calculations of the H-dibaryon binding energy at approximately the same lattice spacing, the forms of the chiral and continuum extrapolations to the physical point are not determined. In this brief report, we consider the constraints on the H-dibaryon imposed by two simple chiral extrapolations. In both instances, the extrapolation to the physical pion mass allows for a bound H-dibaryon or a near-threshold scattering state. Further lattice QCD calculations are required to clarify this situation.Comment: 8 pages, 2 figures, 1 table; revised for the journa