Pion physics at finite volume

We use chiral perturbation theory coupled to electromagnetism in a periodic box to study the impact of volume corrections on pion physics in lattice QCD. We demonstrate that conserved currents can be additively renormalized by infrared effects and construct gauge invariant single particle effective theories to explain these results. In such theories, current renormalization arises from operators involving the zero mode of the gauge field. No contradictions with Ward identities, or low-energy theorems are encountered. We also investigate finite volume corrections to the Compton scattering tensor to study the extraction of pion electromagnetic polarizabilities from lattice QCD. We argue, however, that such results cannot be used to ascertain volume corrections to polarizabilities determined in lattice QCD with background field methods. Connection is lacking because momentum expansions are not permitted in finite volume. Our argument also applies to form factors.