Numerical calculation of the momentum-space gluon propagator in quenched,reduced QCD3

A recently developed method of momentum-space Monte Carlo is applied to compute the momentum-space gluon propagator in quenched, reduced, continuum QCD₃ in axial gauge. There is some evidence that the gluon propagator D_μν(p) is finite as p → 0, which might indicate the existence of a non-perturbative gluon mass.     

High statistics study of the chiral condensate in quenched lattice QCD

We present the results of a high statistics study of the chiral condensate in quenched lattice QCD on an 8⁴ lattice at β = 5.4, 5.5, 5.6, 5.7, 5.8 and 6.0. We see clear evidence for deviation from asymptotic scaling in the range of β considered. Our results are in agreement with the behaviour anticipated from recent Monte Carlo renormalisation group studies of the β-function. We find indications of a common scaling behaviour for the condensate, the string tension and the deconfinement temperature.     

The chiral limit of quenched lattice QCD

We investigate the low mass properties of our quenched QCD data for the range of beta values: 5.70, 6.00, 6.15 and 6.30. The chiral condensate, the ground-state meson spectrum and the scaling behaviour of various quantities are examined. A criterion for assessing at what value of the quark mass finite lattice effects become intolerable is suggested.     

Non-perturbative QCD amplitudes in quenched and eikonal approximations

Even though approximated, strong coupling non-perturbative QCD amplitudes remain very difficult to obtain. In this article, in eikonal and quenched approximations at least, physical insights are presented that rely on the newly-discovered property of effective locality. The present article also provides a more rigorous mathematical basis for the crude approximations used in the previous derivation of the binding potential of quarks and nucleons. Furthermore, the techniques of Random Matrix calculus along with Meijer G-functions are applied to analyze the generic structure of fermionic amplitudes in QCD.     

Non-perturbative quark mass renormalization in quenched lattice QCD

The renormalization factor relating the bare to the renormalization group invariant quark masses is accurately calculated in quenched lattice QCD using a recursive finite-size technique. The result is presented in the form of a product of a universal factor times another factor, which depends on the details of the lattice theory but is easy to compute, since it does not involve any large scale differences. As a byproduct the A-parameter of the theory is obtained with a total error of 8%.     

BK from quenched QCD with exact chiral symmetry

We present a calculation of the standard model DeltaS=2 matrix element relevant to indirect CP violation in K-->pipi decays which uses Neuberger's chiral formulation of lattice fermions. The computation is performed in the quenched approximation on a 16(3) x 32 lattice that has a lattice spacing a approximately 0.1 fm. The resulting bare matrix element is renormalized nonperturbatively. Our main result is B(RGI)(K)=0.87(8)+2+14-1-14, where the first error is statistical, the second is systematic, and the third is Sharpe's estimate of quenching and flavor-SU(3) breaking uncertainties.     

A study of perfect wetting for Potts and Blume-Capel models with correlation inequalities

The so-called perfect wetting phenomenon is studied for theq-state,d2 Potts model. Using a new correlation inequality, a general inequality is established for the surface tension between ordered phases ( ^a,b ) and the surface tension between an ordered and the disordered phases ( ^a,f ) for any even value ofq. This result implies in particular at the transition point _t where the previous phases coexist forq large. This inequality is connected to perfect wetting at the transition point using thermodynamic considerations. The same kinds of results are derived for the Blume-Capel model.     

Numerical study of dense adjoint matter in two color QCD

We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential , for fermions in both fundamental and adjoint representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N = 1 adjoint flavor on a lattice are presented, using both hybrid Monte Carlo and Two-Step Multi-Boson algorithms. It is shown that the sign of the fermion determinant starts to fluctuate once the model enters a phase with non-zero baryon charge density. HMC simulations are not ergodic in this regime, but TSMB simulations retain ergodicity even in the dense phase, and in addition appear to show superior decorrelation. The HMC results for the equation of state and the pion mass show good quantitative agreement with the predictions of chiral perturbation theory, which should hold only for . The TSMB results incorporating the sign of the determinant support a delayed onset transition, consistent with the pattern of symmetry breaking expected for N = 1. Received: 20 June 2000 / Published online: 31 August 2000     

Exact critical behavior of two-dimensional wetting problems with quenched disorder

The wetting transition in the presence of a random substrate is studied in two dimensions, using a restricted solid-on-solid model. The singular part of the quenched free energy and specific heat is calculated exactly by means of the replica trick. Disorder introduces logarithmic corrections to the results of the pure system. The divergent part of the width of the wetting layer is also evaluated: here no corrections to the pure case are obtained. The method employed uses a field-theoretic calculation (in terms of Goldstone diagrams) of the ground-state energy of an effective many-body Hamiltonian. The validity of the replica method is tested numerically.     

Two-point functions of quenched lattice QCD in Numerical Stochastic Perturbation Theory. (II) The gluon propagator in Landau gauge

This is the second of two papers devoted to the perturbative computation of the ghost and gluon propagators in SU(3)$\mathit{SU}(3)$ Lattice Gauge Theory. Such a computation should enable a comparison with results from lattice simulations in order to reveal the genuinely non-perturbative content of the latter. The gluon propagator is computed by means of Numerical Stochastic Perturbation Theory: results range from two up to four loops, depending on the different lattice sizes. The non-logarithmic constants for one, two and three loops are extrapolated to the lattice spacing a→0$a\to 0$ continuum and infinite volume V→∞$V\to \infty$ limits.     

Test of the Skyrme effective field theory using quenched lattice QCD

The Skyrme effective field theory is tested by evaluating nucleon ground-state matrix elements of the correlation functions for two flavor density operators and two pseudoscalar density operators in the Skyrme model and comparing them with results in quenched lattice QCD. The possibility of using quenched lattice QCD to study higher-order terms in effective field theory is also discussed.     

Flavor symmetry breaking and scaling for improved staggered actions in quenched QCD

We present a study of the flavor symmetry breaking in the pion spectrum for the p4-improved fermion action. Three different variants of the p4 action – p4fat3, p4fat7, and p4fat7tad – are compared to the Asqtad and naive staggered actions. To study the pattern of symmetry breaking, we measure all 15 pion masses in the four-flavor staggered theory. The measurements are done on a quenched gauge background, generated using a one-loop improved Symanzik action with β=10/g²=7.40, 7.75, and 8.00, corresponding to lattice spacings of approximately a= 0.31 fm, 0.21 fm, and 0.14 fm. PACS 11.15.Ha; 11.30.Rd; 12.38.Aw; 12.38.-t; 12.38.Gc     

Meson screening masses at high temperature in quenched QCD with improved Wilson Quarks

We report on a lattice investigation of improved quenched Wilson fermions above and below the confinement-deconfinement phase transition. Results on meson screening masses as well as spatial wave functions are presented. Moreover, the meson dispersion relation is studied. Below the critical temperature we do not observe any significant temperature effect while above the data are consistent with a leading free quark behavior. Received: 2 April 2001 / Published online: 8 June 2001