A local factorization of the fermion determinant in lattice QCD

TL;DR

This paper presents a novel local factorization of the fermion determinant in lattice QCD, enabling multilevel Monte Carlo methods with improved signal-to-noise ratios for fermionic observables.

Contribution

It introduces a local factorization approach for the fermion determinant that facilitates multilevel Monte Carlo integration in lattice QCD with Wilson fermions.

Findings

Successful numerical tests on gluonic observables

Enhanced signal-to-noise ratio in disconnected correlator computations

Demonstration of multilevel Monte Carlo potential with fermions

Abstract

We introduce a factorization of the fermion determinant in lattice QCD with Wilson-type fermions that leads to a bosonic action which is local in the block fields. The interaction among gauge fields on distant blocks is mediated by multiboson fields located on the boundaries of the blocks. The resultant multiboson domain-decomposed hybrid Monte Carlo passes extensive numerical tests carried out by measuring standard gluonic observables. The combination of the determinant factorization and of the one of the propagator, that we put forward recently, paves the way for multilevel Monte Carlo integration in the presence of fermions. We test this possibility by computing the disconnected correlator of two flavor-diagonal pseudoscalar densities, and we observe a significant increase of the signal-to-noise ratio due to a two-level integration.