Effects of non-perturbatively improved dynamical fermions in QCD at fixed lattice spacing

TL;DR

This study investigates how non-perturbatively improved dynamical fermions influence various QCD observables at fixed lattice spacing, revealing subtle effects on the hadron spectrum and more significant differences in topological properties.

Contribution

It provides the first detailed comparison of quenched and unquenched QCD using non-perturbatively improved actions at fixed physical lattice size.

Findings

Evidence of charge screening effects.

Minor impact on light hadron spectrum.

Significant differences in topological susceptibility.

Abstract

We present results for the static inter-quark potential, lightest glueballs, light hadron spectrum and topological susceptibility using a non-perturbatively improved action on a $16^3\times 32$ lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units ($\sim 1.7$ fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavours of dynamical quarks. With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied ($M_{PS}/M_{V}\ge0.58$). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.