Electromagnetic Processes in $\chi$EFT

TL;DR

This paper develops electromagnetic current models within chiral effective field theory including nucleons, deltas, and pions up to N$^2$LO, and applies them to neutron capture and nuclear magnetic moments, revealing underpredictions in certain observables.

Contribution

It introduces a chiral EFT framework with explicit deltas for electromagnetic processes in light nuclei, calibrated to specific cross sections and magnetic moments.

Findings

Underpredicts neutron-deuteron radiative capture cross section.

Underpredicts photon circular polarization in neutron-deuteron capture.

Provides a systematic EFT approach including delta isobars.

Abstract

Nuclear electromagnetic currents derived in a chiral-effective-field-theory framework including explicit nucleons, $\Delta$ isobars, and pions up to N$^2$LO, {\it i.e.} ignoring loop corrections, are used in a study of neutron radiative captures on protons and deuterons at thermal energies, and of $A$=2 and 3 nuclei magnetic moments. With the strengths of the $\Delta$-excitation currents determined to reproduce the $n$-$p$ cross section and isovector combination of the trinucleon magnetic moments, we find that the cross section and photon circular polarization parameter, measured respectively in $n$-$d$ and $\vec{n}$-$d$ processes, are significantly underpredicted by theory.