Electromagnetic contribution to the proton-neutron mass splitting

Abstract

We study the electromagnetic contribution to the proton-neutronmass splitting by combining lattice simulations and the modified Cottingham sum rule of Walker-Loud, Carlson, and Miller. This analysis yields an estimate of the isovector nucleon magnetic polarizability as a function of pion mass. The physical value, obtained by chiral extrapolation to the physical pion mass, is βp-n= (−1.12 ± 0.40) × 10−4 fm3,, which is in agreement with the empirical result, albeit with a somewhat smaller error. As a result, we find δMγ p-n= 1.04 ± 0.11 MeV, which represents a significant improvement in precision.