Calculation of two-photon exchange effects for Δ production in electron–proton collisions

We present an evaluation of a two-photon exchange correction to the cross section for unpolarized Δ isobar production in electron–proton collisions, using a relativistic, crossing symmetric and gauge invariant approach. The calculated box and crossed-box diagrams include nucleon and Δ intermediate states. We find a relation between the angular nonlinearity of the two-photon exchange contribution and the value of the γΔΔ coupling constant.