Pion photoproduction in a nonrelativistic theory

TL;DR

This paper develops a nonrelativistic effective field theory to accurately describe pion photoproduction on nucleons, capturing the cusp effect caused by mass differences, and provides detailed amplitude calculations at two loops.

Contribution

It introduces a rigorous nonrelativistic effective field theory with a consistent power counting scheme for pion photoproduction, including two-loop amplitude expressions.

Findings

Derived S- and P-wave multipole amplitudes for all channels.

Captured the pronounced cusp effect due to mass differences.

Provided two-loop level theoretical predictions.

Abstract

The pion and nucleon mass differences generate a very pronounced cusp in the photoproduction reaction of a single pion on the nucleon. A nonrelativistic effective field theory to describe this reaction is constructed. The approach is rigorous in the sense that it is an effective field theory with a consistent power counting scheme. Expressions for the S- and P-wave multipole amplitudes for all four reaction channels at two loops are given.