Proton polarizability contribution: Muonic hydrogen Lamb shift and elastic scattering

The uncertainty in the contribution to the Lamb shift in muonic hydrogen, Delta E-subt arising from proton polarizability effects in the two-photon exchange diagram at large virtual photon momenta is shown large enough to account for the proton radius puzzle. This is because Delta E-subt is determined by an integrand that falls very slowly with very large virtual photon momenta. We evaluate the necessary integral using a set of chosen form factors and also a dimensional regularization procedure which makes explicit the need for a low energy constant. The consequences of our two-photon exchange interaction for low-energy elastic lepton-proton scattering are evaluated and could be observable in a planned low energy lepton-proton scattering experiment planned to run at PSI. (C) 2012 Elsevier B.V. All rights reserved.