HISQ action in dynamical simulations

TL;DR

This paper discusses recent advancements in implementing the HISQ action for dynamical fermion simulations, highlighting improvements in taste symmetry and addressing computational challenges in fermion force calculations.

Contribution

It introduces the application of the HISQ action in dynamical simulations, detailing the improvements and challenges associated with reunitarization and taste symmetry suppression.

Findings

HISQ action reduces taste symmetry violations.

Preliminary results on 2+1+1 flavor ensembles show promising performance.

Challenges in fermion force calculation due to reunitarization are identified.

Abstract

We report on recent progress in employing the Highly Improved Staggered Quark (HISQ) action introduced by the HPQCD/UKQCD collaboration in simulations with dynamical fermions. The HISQ action is an order $a^2$ Symanzik-improved action with further suppressed taste symmetry violations. The improvement in taste symmetry is achieved by introducing Fat7 smearing of the original gauge links and reunitarization (projection to an element of U(3) or SU(3)) followed by Asq-type smearing. Major challenges for calculating the fermion force are related to the reunitarization step. We present a preliminary study of the HISQ action on two 2+1+1 flavor ensembles with the lattice spacing roughly equivalent to the MILC asqtad a=0.125 and 0.09 fm ensembles.