Two-photon exchange from intermediate state resonances in elastic electron-proton scattering

We use a recently developed dispersive approach to compute the two-photon exchange (TPE) correction to elastic electron-proton scattering, including contributions from hadronic J(P) = 1/2(+/-) and 3/2(+/-) resonant intermediate states below 1.8 GeV. For the transition amplitudes from the proton ground state to the resonant excited states we employ new exclusive meson electroproduction data from CLAS at Q(2) less than or similar to 5 GeV2, and we explore the effects of both fixed and dynamic widths for the resonances. Among the resonant states, the N(1520)3/2(-) becomes dominant for Q(2) greater than or similar to 2 GeV2, with a sign opposite to the comparably sized Delta(1232)3/2(+) contribution, leading to an overall increase in the size of the TPE correction to the cross section relative to the nucleon only contribution at higher Q(2) values. The results are in good overall agreement with recent e(+) p to e(-) p cross-section ratio and polarization transfer measurements, and provide compelling evidence for a resolution of the electric to magnetic form factor ratio discrepancy.