FLIC-Overlap Fermions and Topology

TL;DR

This paper demonstrates that FLIC-Overlap fermions, enhanced by APE smearing and an improved field-strength tensor, improve spectral properties and correctly realize topology in lattice QCD simulations.

Contribution

It introduces a highly-improved lattice field-strength tensor within FLIC fermions, improving spectral flow and topological accuracy in overlap fermions.

Findings

Significant reduction in the condition number of the Hermitian-Dirac operator.

Removal of spurious spectral flow crossings caused by lattice artifacts.

Enhanced topological correctness in the fermion sector.

Abstract

APE smearing the links in the irrelevant operators of clover fermions (Fat-Link Irrelevant Clover (FLIC) fermions) provides significant improvement in the condition number of the Hermitian-Dirac operator and gives rise to a factor of two savings in computing the overlap operator. This report investigates the effects of using a highly-improved definition of the lattice field-strength tensor F_mu_nu in the fermion action, made possible through the use of APE-smeared fat links in the construction of the irrelevant operators. Spurious double-zero crossings in the spectral flow of the Hermitian-Wilson Dirac operator associated with lattice artifacts at the scale of the lattice spacing are removed with FLIC fermions composed with an O(a^4)-improved lattice field strength tensor. Hence, FLIC-Overlap fermions provide an additional benefit to the overlap formalism: a correct realization of topology in the fermion sector on the lattice.