Structure of Pion Photoproduction Amplitudes

TL;DR

This paper derives finite energy sum rules for pion photoproduction, evaluates their low energy parts with various models, and develops a Regge-pole expansion model that aligns with both sum rules and high-energy data.

Contribution

It introduces a novel application of finite energy sum rules to pion photoproduction and proposes a Regge-pole model that unifies low and high-energy descriptions.

Findings

Differences in sum rule low energy sides relate to baryon resonance quantum numbers.

Regge theory explains features observed in the sum rules.

A Regge-pole model successfully matches sum rules and high-energy data.

Abstract

We derive and apply the finite energy sum rules to pion photoproduction. We evaluate the low energy part of the sum rules using several state-of-the-art models. We show how the differences in the low energy side of the sum rules might originate from different quantum number assignments of baryon resonances. We interpret the observed features in the low energy side of the sum rules with the expectation from Regge theory. Finally, we present a model, in terms of a Regge-pole expansion, that matches the sum rules and the high-energy observables.