Simulating Full QCD with the Fixed Point Action

TL;DR

This paper presents a novel algorithm for simulating full QCD with the fixed point action, enabling more realistic lattice QCD simulations with physical quark masses and lighter pions.

Contribution

The authors developed and tested a new updating procedure for fixed point actions in lattice QCD, accommodating 2+1 flavors with physical s-quark mass and light u/d-quarks.

Findings

Acceptance rate of ~0.4 in the accept/reject step

Algorithm successfully runs on lattices up to 1.8fm

Simulation includes physical s-quark mass and light pions

Abstract

Due to its complex structure the parametrized fixed point action can not be simulated with the available local updating algorithms. We constructed, coded, and tested an updating procedure with 2+1 light flavors, where the targeted s-quark mass is at its physical value while the u- and d-quarks should produce pions lighter than 300MeV. In the algorithm a partially global gauge update is followed by several accept/reject steps, where parts of the determinant are switched on gradually in the order of their expenses. The trial configuration that is offered in the last, most expensive, stochastic accept/reject step differs from the original configuration by a Metropolis + over-relaxation gauge update over a sub-volume of ~(1.3 fm)^4. The acceptance rate in this accept/reject step is ~0.4. The code is optimized on different architectures and is running on lattices with L=1.2fm and 1.8fm at a resolution of a=0.15fm.