Pietro Rossi

The QCD finite temperature transition and hybrid Monte Carlo

Using the hybrid Monte Carlo method we consider lattice quantum chromodynamics with Kogut-Susskind staggered fermions on 43 × 4, 63 × 4, 83 × 4 lattices with m = 0.1. Applying finite size scaling methods for a first-order phase transition we find some evidence for a two-phase state.

A comparison of a variety of matrix inversion algorithms for Wilson fermions on the lattice

Abstract We compare a number of numerical algorithms for inverting the lattice Dirac operator in the Wilson formulation. Among the algorithms that we have studied, the Fourier preconditioned conjugate gradient is the most robust and efficient algorithm near κ c , even taking into account the overhead due to gauge fixing.

Quenched hadronic screening lengths at high temperature

Abstract We measure the spatial screening lengths of local meson and baryon operators in the deconfined phase of pure SU(3) gauge theory. We work on a lattice of size 8 2 ×24×4 at a temperature T =1.5 T c , with T c the deconfinement temperature. The scre ening lengths are found in parity doublets and the chiral projections for the meson and baryon correlation functions are consistent with unbroken chiral symmetry. Our results are in good quantitative agreement with the full QCD results of Gottlieb et al. at the same temperature.

Measure of autocorrelation times of local hybrid Monte Carlo algorithm for lattice QCD

Abstract We report on a study of the autocorrelation times of the local version of the hybrid Monte Carlo (LHMC) algorithm for pure gauge SU(3). We compare LHMC to standard multi-hit Metropolis and to the global version of the same HMC. For every algorithm we measure the autocorrelation time (τ) for a variety of observables and the string tension (σ) as a function of β . The measurements performed on 8 4 and 16 4 lattices indicate that the autocorrelation time of LHMC is significantly shorter than for the other two algorithms.We report on a study of the autocorrelation times of the local version of the Hybrid Monte Carlo (LHMC) algorithm for pure gauge

Hybrid Monte Carlo and quantum chromodynamics

SU(3)

Monte-Carlo simulation of CP(N-1) models

. We compare LHMC to standard multi-hit Metropolis and to the global version of the same HMC. For every algorithm we measure the autocorrelation time for a variety of observables and the string tension as a function of beta. The measurements performed on 8^4 and 16^4 lattices indicate that the autocorrelation time of LHMC is significantly shorter than for the other two algorithms.

The chiral limit and phase structure of QCD with Wilson fermions

Abstract In this paper we study the properties of the hybrid Monte Carlo algorithm applied to lattice quantum chromodynamics including the dynamical effects of fermions. We find that this “exact” method performs very well on 44 lattices, and shows considerable promise for being a practicable means with which to undertake realistic Monte Carlo computations of fermionic systems.

Hadron spectrum and matrix elements in QCD with dynamical Wilson fermions at 6/g2=5.3.

Numerical simulations of two-dimensional CP{sup {ital N}{minus}1} models are performed at {ital N}=2, 10, and 21. The lattice action adopted depends explicitly on the gauge degrees of freedom and shows precocious scaling. Our tests of scaling are the stability of adimensional physical quantities (second moment of the correlation function versus inverse mass gap, magnetic susceptibility versus square correlation length) and rotation invariance. Topological properties of the models are explored by measuring the topological susceptibility and by extracting the Abelian string tension. Several different (local and nonlocal) lattice definitions of topological charge are discussed and compared. The qualitative physical picture derived from the continuum 1/{ital N} expansion is confirmed, and agreement with quantitative 1/{ital N} predictions is satisfactory. Variant (Symanzik-improved) actions are considered in the CP{sup 1}{approx}O(3) case and agreement with universality and previous simulations (when comparable) is found. The simulation algorithm is an efficient picture of over-heat-bath and microcanonical algorithms. The dynamical features and critical exponents of the algorithm are discussed in detail.

Gribov copies in lattice QCD

Abstract We present data for the simulation of QCD with two flavours of Wilson fermions on an 83×4 lattice for various values of the coupling β and the hopping parameter κ. The emphasis is on the approach to the chiral limit and its interplay with the finite temperature transition for the system. We find that the point β c ∗ =5.0, κ c ∗ =0.175 in the β-κ plane represents the intersection of the finite temperature transition and the chiral limit. For lower values of β it is possible to approach the chiral limit in the confined phase as κ→κc, whereas at higher values of β the system undergoes a finite temperature deconfining transition at non-zero quark mass. The value of β c ∗ increases with lattice size. For example, we show that it is possible to reach the unbroken chiral limit on an 84 lattice at β=5.0.

On simulating complex actions

We present results of a lattice simulation of quantum chromodynamics with two degenerate flavors of dynamic Wilson fermions at