Chiral perturbation theory of muonic-hydrogen Lamb shift: Polarizability contribution

Abstract

The proton polarizability effect in the muonic-hydrogen Lamb shift comes out as a prediction of baryon chiral perturbation theory at leading order and our calculation yields (Formula presented.). This result is consistent with most of evaluations based on dispersive sum rules, but it is about a factor of 2 smaller than the recent result obtained in heavy-baryon chiral perturbation theory. We also find that the effect of Δ(1232)-resonance excitation on the Lamb shift is suppressed, as is the entire contribution of the magnetic polarizability; the electric polarizability dominates. Our results reaffirm the point of view that the proton structure effects, beyond the charge radius, are too small to resolve the 'proton radius puzzle'. © 2014 The Author(s).