Magnetic polarisability of octet baryons near the physical quark-mass point

TL;DR

This study computes the magnetic polarisabilities of octet baryons near physical quark masses using lattice QCD, overcoming previous computational challenges by removing exceptional configurations, and finds results consistent with chiral perturbation theory.

Contribution

First lattice QCD calculation of octet baryon magnetic polarisabilities near physical quark masses with a novel method to eliminate exceptional configurations.

Findings

Good agreement with chiral perturbation theory

Light up and down quarks are more problematic than strange quarks

Exceptional configuration removal improves precision of results

Abstract

The magnetic polarisabilities of octet baryons are calculated close to the physical quark-mass point using the background field method in lattice QCD. This first calculation draws on the identification and elimination of exceptional configurations that have hindered previous attempts. The origin of the exceptional configuration problem lies in the use of a Wilson-type fermion action on electro-quenched gauge field configurations, where the dynamical-fermion gauge-field generation algorithm the electric charges of the quarks. Changes in the fermion determinant that would suppress some gauge fields in the background magnetic field are neglected, leaving improbable gauge fields that generate large additive mass renormalisations which manifest as significant outliers in correlation-function distributions. An algorithm for the systematic identification and removal of these exceptional configurations is described. We find the light up and down quarks to be problematic, particularly the up quark with its larger electric charge. The heavier mass of the strange quark protects the hyperon correlation functions to some extent. However, these also benefit from the removal of exceptional configurations. In many cases, the magnetic polarisability is calculated with good precision. We find our results to be in accord with the behaviour anticipated by chiral perturbation theory.