Electromagnetic Structure of Two- and Three-Nucleon Systems: An Effective Field Theory Description

Abstract

I discuss the use of chiral effective field theory (χEFT) to describe electromagnetic reactions in the two- and three-nucleon systems. I review the results of χEFT power counting for charge and current operators up to [Formula: see text] relative to leading order, before showing that renormalization-group arguments imply that short-distance electromagnetic operators play a larger role than suggested by this standard counting. A detailed examination of χEFT's predictions for the electromagnetic form factors of deuterium and the trinucleons, and for the threshold captures np→dγ and nd→tγ, enables a critical appraisal of the theory's performance in these contexts. Recent χEFT calculations using the [Formula: see text] chiral perturbation theory (χPT) potential yielded both form factors that agree with experimental data for Q2<0.25 GeV2 and an excellent description of the challenging threshold captures. Short-distance M1 operators are essential to this success, and the addition of a short-distance part of the nucleon–nucleon charge operator produces precise predictions of the deuteron charge and quadrupole form factors in this kinematic domain.