We consider the Rational Hybrid Monte Carlo algorithm for performing exact 2+1 flavour fermion simulations. The specific cases of asqtad and domain wall fermions are considered. We find that in both cases the naïve performance is similar to conventional hybrid algorithms.

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We propose a strategy for conducting lattice QCD simulations at fixed volume but variable quark mass so as to investigate the physical effects of dynamical fermions. We present details of techniques which enable this to be carried out effectively, namely the tuning in bare parameter space and efficient stochastic estimation of the fermion determinant. Preliminary results and tests of the method are presented. We discuss further possible applications of these techniques. 12.38.Gc, 11.15.Ha, 02.70.Lq

We present the first results for the static quark potential and the light hadron spectrum using dynamical fermions at ␤ϭ5.2 using an O(a) improved Wilson fermion action together with the standard Wilson plaquette action for the gauge part. Sea quark masses were chosen such that the pseudoscalar-vector mass ratio, m PS /m V , varies from 0.86 to 0.67. Finite-size effects are studied by using three different volumes 8 3 ϫ24, 12 3 ϫ24, and 16 3 ϫ24. Comparing our results to previous ones obtained using the quenched approximation, we find evidence for sea quark effects in quantities such as the static quark potential and vector-pseudoscalar hyperfine splitting. ͓S0556-2821͑99͒00613-X͔ PACS number͑s͒: 12.38. Gc, 12.40.Yx The lattice action can be split into a pure gauge part S G and a fermionic part S F :where PHYSICAL REVIEW D, VOLUME 60, 034507 0556-2821/99/60͑3͒/034507͑15͒/$15.00