QED with massive photons for precision physics: zero modes and first result for the hadron spectrum

TL;DR

This paper discusses the use of a massive photon in lattice QED to improve the precision of low-energy hadronic observable calculations, focusing on zero mode issues and photon mass corrections.

Contribution

It introduces a controlled method for removing the photon mass in lattice QED, addressing zero mode contributions and volume extrapolations for precise hadron spectrum calculations.

Findings

Zero mode contributions are well understood and controlled.

Photon mass corrections can be reliably extrapolated.

Finite volume effects are manageable with the proposed approach.

Abstract

The current precision reached by lattice QCD calculations of low-energy hadronic observables, requires not only the introduction of electromagnetic corrections, but also control over all the potential systematic uncertainties introduced by the lattice version of QED. Introducing a massive photon as an infrared regulator in lattice QED, provides a well defined theory, dubbed QEDM, amenable to numerical evaluation [arXiv:1507.08916]. The photon mass is removed through extrapolation. In this contribution we scrutinise aspects of QEDM such as the presence and fate of the zero modes contributions and we describe the determination of the photon mass corrections in finite and infinite volume. We demonstrate that the required extrapolations are well controlled using numerical data obtained on two ensembles which only differ in volume.