Form factors in lattice QCD

TL;DR

This paper discusses lattice QCD calculations of hadron form factors, highlighting recent methods to improve accuracy and control systematic uncertainties, especially for nucleon axial charge and pion charge radius.

Contribution

It introduces new techniques like summed correlation functions and twisted boundary conditions to reduce systematic errors in lattice QCD form factor computations.

Findings

Lattice QCD results for hadron masses agree well with experiments.

Systematic uncertainties in nucleon form factors are addressed with novel methods.

Preliminary results for nucleon axial charge show promising improvements.

Abstract

Lattice simulations of QCD have produced precise estimates for the masses of the lowest-lying hadrons which show excellent agreement with experiment. By contrast, lattice results for the vector and axial vector form factors of the nucleon show significant deviations from their experimental determination. We present results from our ongoing project to compute a variety of form factors with control over all systematic uncertainties. In the case of the pion electromagnetic form factor we employ partially twisted boundary conditions to extract the pion charge radius directly from the linear slope of the form factor near vanishing momentum transfer. In the nucleon sector we focus specifically on the possible contamination from contributions of higher excited states. We argue that summed correlation functions offer the possibility of eliminating this source of systematic error. As an illustration of the method we discuss our results for the axial charge, gA, of the nucleon.