Dynamical overlap fermion at fixed topology

TL;DR

This paper presents a method for dynamical overlap fermion simulations at fixed topology, using extra Wilson fermions to prevent topological boundary crossings, resulting in faster simulations and analysis of finite volume effects.

Contribution

The authors introduce a fixed-topology simulation technique with extra Wilson fermions, improving efficiency and enabling study of topological effects in lattice QCD.

Findings

Simulations are significantly faster with fixed topology.

Topological charge remains conserved during simulations.

Finite volume effects due to fixed topology are analyzed.

Abstract

We launched a project to perform dymanical fermion simulations using the overlap fermion formulation for sea quarks. In order to avoid the appearace of near-zero modes of the hermitian Wilson-Dirac operator $H_W$, we introduce a pair of extra Wilson fermions with a large negative mass term. Crossing of the topological boundary is then strictly prohibited, and the topological charge is conserved during simulations. It makes the simulations substantially faster compared to the algorithms which allow the topology change. We discuss on the finite volume effects due to the fixed global topology.