Simple check of the vacuum structure in full QCD lattice simulations

TL;DR

This paper examines whether the vacuum structure in unquenched 2-flavour QCD lattice simulations significantly differs from quenched QCD by analyzing topological susceptibility data across various sea-quark masses.

Contribution

It provides a simple method to compare vacuum structures in lattice QCD simulations using topological susceptibility data, highlighting potential deviations from quenched QCD.

Findings

Discretization effects may still be large in dynamical simulations.

Vacuum structure in 2-flavour QCD may differ from 3-flavour or 2+1-flavour QCD.

The analysis suggests either large discretization effects or genuine differences in vacuum structure.

Abstract

Given the increasing availability of lattice data for (unquenched) QCD with $N_f=2$, it is worth while to check whether the generated vacuum significantly deviates from the quenched one. I discuss a specific attempt to do this on the basis of topological susceptibility data gained at various sea-quark masses, since for this observable detailed predictions are available. The upshot is that either discretization effects in dynamical simulations are still untolerably large or the vacuum structure in 2-flavour QCD substantially deviates from that in the theory with 3 (or 2+1) light quarks.