Photoabsorption off nuclei with self consistent vertex corrections

TL;DR

This paper presents a covariant many-body approach to photoproduction off nuclei, incorporating in-medium pion exchange with vertex corrections, and predicts an attractive isobar mass shift of about 50 MeV at nuclear saturation density.

Contribution

It introduces a self-consistent, covariant framework for pion and isobar propagation in nuclear matter, including in-medium pion exchange with vertex corrections and gauge invariance.

Findings

Predicts a 50 MeV attractive mass shift for the isobar at saturation density.

First consistent evaluation of in-medium pion t-channel exchange with vertex corrections.

Maintains electromagnetic gauge invariance through Ward identities.

Abstract

We study photoproduction off nuclei based on a self consistent and covariant many body approach for the pion and isobar propagation in infinite nuclear matter. For the first time the t-channel exchange of an in-medium pion is evaluated in the presence of vertex correction effects consistently. In particular the interference pattern with the s-channel in-medium nucleon and isobar exchange contribution is considered. Electromagnetic gauge invariance is kept as a consequence of various Ward identities obeyed by the computation. Adjusting the set of Migdal parameters to the data set we predict an attractive mass shift for the isobar of about 50 MeV at nuclear saturation density.