Exploring QCD at small sea quark masses with improved Wilson-type quarks

TL;DR

This paper investigates small sea quark masses in two-flavor QCD using improved Wilson-type quarks, addressing algorithmic stability issues and analyzing finite-size and chiral effects on meson masses.

Contribution

It demonstrates the effectiveness of the BiCGStab(DS-L) algorithm for small quark masses and studies finite-size and chiral properties in improved Wilson-type lattice QCD.

Findings

BiCGStab(DS-L) improves stability at small quark masses

Identification of singular spikes in HMC at moderate step sizes

Finite-size effects and chiral properties of mesons analyzed

Abstract

We explore the region of small sea quark masses below $m_{PS}/m_V=0.5$ in two-flavor QCD using a mean-field improved clover quark action and an RG-improved gauge action at $a \simeq 0.2$ fm on $12^3 \times 24$ and $16^3 \times 24$ lattices. We find that instability of the standard BiCGStab algorithm at small quark masses can be mostly removed by the BiCGStab(DS-$L$) algorithm, which employs $L$-th minimal residual polynomials with a dynamical selection of $L$. We also find singular spikes of $\Delta H$ in the HMC algorithm at moderate values of $\Delta\tau$. Nature of the spike is studied. We also study finite-size effects and chiral properties of meson masses.