Taste breaking in the minimally doubled Karsten-Wilczek action and its tree-level improvement

TL;DR

This paper investigates taste breaking effects in minimally doubled Karsten-Wilczek fermions in lattice QCD, exploring tree-level improvements and non-perturbative tuning to reduce discretization errors and approach the continuum limit.

Contribution

It provides a detailed numerical study of taste breaking in the Karsten-Wilczek action, including a comparison of improved and unimproved formulations and their continuum behavior.

Findings

Tree-level Naik improvement reduces discretization errors.

Non-perturbative tuning improves taste symmetry restoration.

Taste breaking decreases as lattice spacing approaches zero.

Abstract

Minimally doubled fermion actions offer a discretization for two-flavor Quantum Chromodynamics without rooting, but retaining a U(1) chiral symmetry at the same time. The price to pay is a breaking of the hypercubic symmetry, which requires the inclusion and tuning of new counterterms. Similar to staggered quarks, these actions suffer from taste breaking. We perform a mixed action numerical study with the Karsten-Wilczek formulation of minimally doubled fermions on 4stout staggered configurations, generated with physical quark masses, covering a broad range of lattice spacings. We consider a tree-level spatial Naik improvement to mitigate discretization errors. We carry out a non-perturbative tuning of the KW action with and without improvement, and investigate the taste breaking and the approach to the continuum limit.