Preserving Local Gauge Invariance with t-Channel Regge Exchange

Abstract: Considering single-meson photo- and electroproduction off a baryon, it is shown how to restore local gauge invariance that was broken by replacing standard Feynman-type meson exchange in the t-channel by exchange of a Regge trajectory. This is achieved by constructing a contact current whose four-divergence cancels the gauge-invariance-violating contributions resulting from all states above the base state on the Regge trajectory. To illustrate the procedure, modifications necessary for the process $\gamma +p \to K⁺ + \Sigma<sup>{*0}$ are discussed in some detail. We also provide the general expression for the contact current for an arbitrary reaction.