Electromagnetic Processes in $χ$EFT

Nuclear electromagnetic currents derived in a chiral-effective-field-theory framework including explicit nucleons, $Δ$ 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 $Δ$-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.

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