Electromagnetic and spin polarisabilities in lattice QCD

TL;DR

This paper explores how to extract electromagnetic and spin polarisabilities of nucleons using lattice QCD, addressing finite volume effects and providing methods applicable to various QCD simulation types.

Contribution

It introduces an external field method for measuring all nucleon polarisabilities in lattice QCD and derives extrapolation formulas for finite volume and different QCD approximations.

Findings

Polarisabilities depend strongly on lattice volume and quark masses.

Finite volume effects can cause ~10% deviation from infinite volume results.

The method applies to full, partially-quenched, and quenched QCD simulations.

Abstract

We discuss the extraction of the electromagnetic and spin polarisabilities of nucleons from lattice QCD. We show that the external field method can be used to measure all the electromagnetic and spin polarisabilities including those of charged particles. We then turn to the extrapolations required to connect such calculations to experiment in the context of finite volume chiral perturbation theory. We derive results relevant for lattice simulations of QCD, partially-quenched QCD and quenched QCD. Our results for the polarisabilities show a strong dependence on the lattice volume and quark masses, typically differing from the infinite volume limit by ~10% for current lattice volumes and quark masses.