Distance between various discretized fermion actions

TL;DR

This paper investigates the leading order mixed-action effect in lattice QCD using various discretized fermion actions across different lattice spacings, revealing how the effect varies with sea and valence fermion choices.

Contribution

It provides a systematic analysis of the mixed-action effect across multiple fermion discretizations and lattice spacings, highlighting the dependence on sea fermion chiral symmetry.

Findings

$ riangle_{ m mix}$ decreases as the fourth power of lattice spacing for chiral sea fermions.

$ riangle_{ m mix}$ is significantly larger with non-chiral sea fermions like clover.

The effect's behavior depends strongly on the choice of sea fermion action.

Abstract

We present the leading order mixed-action effect $\Delta_{\rm mix}\equiv m_{\pi,{\rm vs}}^2-\frac{m_{\pi,{\rm vv}}^2+m_{\pi,{\rm ss}}^2}{2}$ using HISQ, clover or overlap valence fermion actions on gauge ensembles using various sea fermion actions across a widely-used lattice spacing range $a\in [0.04,0.19]$~fm. The results suggest that $\Delta_{\rm mix}$ decreases as the fourth order of the lattice spacing on the gauge ensembles with dynamical chiral sea fermions, such as Domain wall or HISQ fermions. When a clover sea fermion action which has explicit chiral symmetry breaking is used in the ensemble, $\Delta_{\rm mix}$ can be much larger regardless of the valence fermion action used.