Electromagnetic mass differences of hadrons

Starting from the Cottingham formula, the problem of the ΔI=1 and ΔI=2 mass differences of the pseudoscalar and vector mesons, (1/2+) baryon octet and (3/2+) decuplet are examined in the framework of Harari's approach. The Born and the transition terms of all these particles are calculated using a «low frequency» limit which comes essentially from the strong suppression of high q2 values in the Cottingham integral due to the form factors; in this limit we find a «universal» relation between both the electric and the magnetic contributions of the Born terms to the two gauge-invariant parts on the forward spin-nonflip amplitude for the Compton scattering. The residue function of the A2 Regge pole β(q2) is calculated via FESR for the Compton scattering of K-mesons. The application of FESR to (p-n) mass difference is critically examined. The connection with the residues of all the other particles is obtained with the use of the «universality» hypothesis for the coupling of A2 Regge pole with mesons and baryons proposed by Cabibbo, Horowitz and Ne'eman. We find that the inelastic terms thus evaluated give always a contribution of the right sign to the e.m. mass differences. The final numerical results are in striking agreement with experiment. © 1969 Società Italiana di Fisica.