Taste symmetry breaking with HYP-smeared staggered fermions

TL;DR

This study demonstrates that HYP smearing significantly reduces taste symmetry breaking in staggered fermions, improving discretization effects and enabling more accurate lattice QCD calculations at finer lattice spacings.

Contribution

The paper provides a detailed comparison showing HYP smearing reduces taste breaking more effectively than unimproved and asqtad-improved staggered fermions, especially at small lattice spacings.

Findings

Taste breaking reduced by a factor of 4-7 with HYP smearing.

Discretization effects of order ${ m O}(a^2 p^2)$ are markedly decreased.

Taste-breaking in pion spectrum is reduced by a factor of 2.5-3 compared to asqtad.

Abstract

We study the impact of hypercubic (HYP) smearing on the size of taste breaking for staggered fermions, comparing to unimproved and to asqtad-improved staggered fermions. As in previous studies, we find a substantial reduction in taste-breaking compared to unimproved staggered fermions (by a factor of 4-7 on lattices with spacing $a\approx 0.1 $fm). In addition, we observe that discretization effects of next-to-leading order in the chiral expansion (${\cal O}(a^2 p^2)$) are markedly reduced by HYP smearing. Compared to asqtad valence fermions, we find that taste-breaking in the pion spectrum is reduced by a factor of 2.5-3, down to a level comparable to the expected size of generic ${\cal O}(a^2)$ effects. Our results suggest that, once one reaches a lattice spacing of $a\approx 0.09 $fm, taste-breaking will be small enough after HYP smearing that one can use a modified power counting in which ${\cal O}(a^2) \ll {\cal O}(p^2)$, simplify fitting to phenomenologically interesting quantities.