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 ≅ 0.2 fm on 12 3 × 24 and 16 3 × 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 Δ H in the HMC algorithm at moderate values of Δτ. Nature of the spike is studied. We also study finite-size effects and chiral properties of meson masses.