Isospin symmetry breaking and the neutron-proton mass difference

Abstract

QCD sum rules using polynomial kernels are used to evaluate the strong part of the proton-neutron mass difference DeltaM_np in a model independent fashion. The result for the mass difference turns out to depend sensitively on the value of the four quark condensate and reproduces the experimental value of DeltaM_np for ~ 2^2.Comment: Arguments detailed. Two references added. Version to appear in Physical Review C. DOI:10.1103/PhysRevC.00.00520