Exact 2+1 flavour RHMC simulations

TL;DR

The paper investigates exact 2+1 flavour simulations using Rational Hybrid Monte Carlo (RHMC) for ASQTAD and domain wall fermions. It demonstrates that RHMC, by employing rational approximations to non-integer fermion powers, maintains exact heatbath and acceptance steps while tolerating controlled MD integration errors, enabling efficient 2+1 simulations with exactness. For ASQTAD, a force-term organization reduces overhead, making RHMC competitive with the R algorithm while providing exact results; for domain wall fermions, a field-splitting strategy and Sexton–Weingarten integration render 2+1 RHMC feasible, with initial results showing strong compatibility with this formulation. Overall, RHMC offers an exact, efficient alternative to extrapolation-based or noisy estimators, enabling Hasenbusch-type force reductions and scalable performance on large lattices.

Abstract

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 naive performance is similar to conventional hybrid algorithms.