Cutoff-effects in the spectrum of dynamical Wilson fermions

TL;DR

This paper studies how lattice spacing affects the eigenvalues of the Wilson-Dirac operator in dynamical fermion simulations, revealing cutoff-effects that impact computational algorithms and correlation function evaluations.

Contribution

It identifies cutoff-effects as the cause of very small eigenvalues in dynamical Wilson fermions and demonstrates their dependence on lattice spacing.

Findings

More small eigenvalues are observed at coarser lattice spacing.

Finer lattice spacing reduces cutoff-effects and small eigenvalues.

Cutoff-effects significantly influence HMC algorithms and fermionic correlators.

Abstract

We investigate the low-lying eigenvalues of the improved Wilson-Dirac operator in the Schroedinger functional with two dynamical quark flavors. At a lattice spacing of approximately 0.1 fm we find more very small eigenvalues than in the quenched case. These cause problems with HMC-type algorithms and in the evaluation of fermionic correlation functions. Through a simulation at a finer lattice spacing we are able to establish their nature as cutoff-effects