Revisiting gauge invariance and Reggeization of pion exchange

TL;DR

This paper examines the gauge invariance of Reggeized pion exchange in high-energy light meson photoproduction, ensuring consistency with current conservation and reconciling different channel dynamics within Regge theory.

Contribution

It demonstrates that gauge-invariant amplitudes for even spin J≥2 exchanges are analytic at J=0 and interpretable via nucleon electric currents, linking s-, u-, and t-channel dynamics.

Findings

Gauge-invariant amplitudes are analytic at J=0.

Reconciliation of s-, u-, and t-channel dynamics.

Consistency with Regge theory and current conservation.

Abstract

The Reggeized pion is expected to provide the main contribution to the forward cross section in light meson photoproduction reactions with charge exchange at high energies. We discuss the Reggeization of pion exchange in charged pion photoproduction with an emphasis on consistency with current conservation. We show that the gauge-invariant amplitude for the exchange of a particle with generic even spin $J\geq 2$ in the $t$-channel is analytic at $J=0$, and that it can be interpreted in terms of the nucleon electric current. This enables us to reconcile the dynamics in the $s$- and $u$-channel, which involves also nucleon exchanges, with the amplitude expressed in terms of $t$-channel partial waves, as required by Regge theory.