Cottingham formula for the electromagnetic self-energy contribution to   M_p - M_n
  We provide an update of the determination of the electromagnetic self-energy contribution to M_p - M_n based upon Cottingham's Formula. A technical oversight in the literature is uncovered: the application of the Cottingham Formula requires the use of a subtracted dispersion integral; an argument to evade the subtraction function was presented; the argument was based on false assumptions about the scaling violations of the parton model, a point first mentioned by J. C. Collins. We elucidate this point and utilize low-energy effective theory to relate the unknown subtraction function to the nucleon isovector magnetic polarizability. This allows us to provide the first reliable determination of dM = 1.30(03)(47) MeV [1]. 
Andre Walker-Loud, Carl E. Carlson, Gerald A. Miller
hep-lat hep-ph nucl-th