Electromagnetic Mass Differences and Regge Phenomenology

We examine the electromagnetic mass differences of hadrons by a phenomenological analysis of the forward virtual Compton amplitude. In addition to the usual elastic contribution, we consider in detail the contribution from ${A_2}^0$ Regge exchange for $I=1\mathrm{}$ mass differences and possible contributions from non-Regge behavior for this weak amplitude in the asymptotic region. In the approximation of neglecting the inelastic resonant spectrum in Compton scattering, the contribution of the pure Regge exchange to the subtraction term for any $I=1\mathrm{}$ mass difference can be related to a ratio of the ${A_2}^0$ residue functions (hence independent of the target) and the relevant elastic form factors. This analysis suggests that a large Regge contribution requires comparable longitudinal and transverse electroproduction cross sections at high energy for small spacelike virtual photon mass. The tadpole model is also examined from the observation that certain linear combinations of $I=1\mathrm{}$ mass differences with just the ${A_2}^0$ Regge pole removed can be formulated in terms of unsubtracted dispersion relations and are presumably satisfied by retaining just the elastic contribution. The $\frac{F}{D}$ ratio that we calculate in this way for the tensor-meson couplings to baryons agrees with that obtained from high-energy experiments. From a superconvergence relation it is argued that there is a fixed pole in the helicity-flip crossed-channel Compton amplitude at $J=0\mathrm{}$, $I=1\mathrm{}$, the experimental consequences of which are discussed.