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

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 $\hat{I}”H$ in the HMC algorithm at moderate values of $\hat{I}”\ddot{I}„$. Nature of the spike is studied. We also study finite-size effects and chiral properties of meson masses.

3 pages, 4 figures, Lattice2002(spectrum)