Simulations with different lattice Dirac operators for valence and sea quarks

TL;DR

This paper explores a mixed lattice QCD approach using different Dirac operators for sea and valence quarks to improve simulations in the chiral regime, deriving relevant actions and effective theories.

Contribution

It introduces a mixed action framework with Wilson sea and Ginsparg-Wilson valence quarks, deriving the Symanzik action and chiral Lagrangian including O(a) corrections.

Findings

Derived the local Symanzik action to O(a) for mixed theories

Constructed the low energy chiral effective Lagrangian with O(a) terms

Provided a method to fit lattice data and extract Gasser-Leutwyler coefficients

Abstract

We discuss simulations with different lattice Dirac operators for sea and valence quarks. A goal of such a "mixed" action approach is to probe deeper the chiral regime of QCD by enabling simulations with light valence quarks. This is achieved by using chiral fermions as valence quarks while computationally inexpensive fermions are used in the sea sector. Specifically, we consider Wilson sea quarks and Ginsparg-Wilson valence quarks. The local Symanzik action for this mixed theory is derived to O(a), and the appropriate low energy chiral effective Lagrangian is constructed, including the leading O(a) contributions. Using this Lagrangian one can calculate expressions for physical observables and determine the Gasser-Leutwyler coefficients by fitting them to the lattice data.