Choice of Integrator in the Hybrid Monte Carlo Algorithm

We study efficiency of higher order integrator schemes for the hybrid Monte Carlo (HMC) algorithm. Numerical tests are performed for Quantum Chromo Dynamics (QCD) with two flavors of Wilson fermions. We compare 2nd, 4th and 6th order integrators at various quark masses. The performance depends on both volume and quark mass. On currently accessible large lattices ($V \sim 24^4$), higher order integrators can be more efficient than the 2nd order one only in heavy quark region, $m_q a > 0.3$. Thus we conclude that for most full QCD simulations, except for heavy quark case, the usual 2nd order integrator is the best choice.