Computation of the electromagnetic pion form factor from lattice QCD in the epsilon regime

TL;DR

This paper computes the electromagnetic pion form factor using lattice QCD in the epsilon regime, effectively canceling dominant finite volume effects to match experimental charge radius results.

Contribution

It introduces a method to automatically cancel dominant finite volume effects in lattice QCD calculations of the pion form factor in the epsilon regime.

Findings

Finite volume effects are effectively canceled by ratio techniques.

Lattice data agrees with theoretical predictions.

Extracted pion charge radius matches experimental values.

Abstract

We calculate the electromagnetic pion form factor in lattice QCD with 2+1 flavors of the dynamical overlap quarks. Up and down quark masses are set below their physical values so that the system is in the so-called epsilon regime with the small size of our lattice ~ 1.8 fm. The finite volume corrections are generally expected to be ~ 100% in the epsilon regime. We, however, find a way to automatically cancel the dominant part of them. Inserting non-zero momenta and taking appropriate ratios of the two and three point functions, we can eliminate the contribution from the zero-momentum pion mode. Then the remaining finite volume effect is a small perturbation from the non-zero modes. Our lattice data agree with this theoretical prediction and the extracted pion charge radius is consistent with the experiment.