Progress on four flavor QCD with the HISQ action

TL;DR

This paper reports recent progress in generating gauge configurations using the HISQ action, highlighting technical improvements and presenting results on hadron properties and topological features.

Contribution

The paper details advancements in handling reunitarization in the HISQ action and provides new lattice results at multiple spacings with physical quark masses.

Findings

Reduced pion taste splittings observed.

Accurate light hadron mass calculations.

Consistent topological susceptibility measurements.

Abstract

We describe recent progress on generation of gauge configurations using the Highly Improved Staggered Quark (HISQ) action that was designed by the HPQCD/UKQCD collaboration. The HISQ action requires two levels of smearing with a reunitarization of the links before the second smearing. We describe how we deal with the occurrence of occasional large forces arising from the reunitarization step. The MILC collaboration is currently generating ensembles with approximate lattice spacings of 0.15, 0.12, 0.09, and 0.06 fm, with the strange and charm quark masses close to their physical values and the mass of the light quarks m_l set to 0.2 m_s. We present recent results for pion taste splittings, light hadron masses, the static potential, the eta_c dispersion relation and the topological susceptibility.