Impact of large cutoff-effects on algorithms for improved Wilson fermions

TL;DR

This study examines how large cutoff-effects impact algorithms for improved Wilson fermions in lattice QCD, showing that reducing lattice spacing alleviates algorithmic issues caused by spectral cutoff-effects.

Contribution

The paper demonstrates that algorithmic problems in dynamical fermion simulations are linked to cutoff-effects in the Wilson-Dirac spectrum and are mitigated at finer lattice spacings.

Findings

Large cutoff-effects cause algorithmic problems at coarser lattice spacings.

Reducing lattice spacing to about 0.07 fm alleviates these issues.

Problems are not specific to the Schroedinger functional setup.

Abstract

As a feasibility study for a scaling test we investigate the behavior of algorithms for dynamical fermions in the N_f=2 Schroedinger functional at an intermediate volume of 1 fm^4. Simulations were performed using HMC with two pseudo-fermions and PHMC at lattice spacings of approximately 0.1 and 0.07 fm. We show that some algorithmic problems are due to large cutoff-effects in the spectrum of the improved Wilson-Dirac operator and disappear at the smaller lattice spacing. The problems discussed here are not expected to be specific to the Schroedinger functional.