Magnetic structure of few-nucleon systems at high momentum transfers in a chiral effective field theory approach
Alex Gnech, R. Schiavilla
Abstract
The five low-energy constants (LECs) in the electromagnetic current derived in chiral effective field theory ($\ensuremath{\chi}\mathrm{EFT}$) up to one loop are determined by a simultaneous fit to the $A=2\ensuremath{-}3$ nuclei magnetic moments and to the deuteron magnetic form factor and threshold electrodisintegration at backward angles over a wide range of momentum transfers. The resulting parametrization then yields predictions for the $^{3}\mathrm{He}/^{3}\mathrm{H}$ magnetic form factors in excellent accord with the experimental values for momentum transfers ranging up to $\ensuremath{\approx}0.8$ $\mathrm{GeV}/c$, beyond the expected regime of validity of the $\ensuremath{\chi}\mathrm{EFT}$ approach. The calculations are based on last-generation two-nucleon interactions including high orders in the chiral expansion and derived by Entem, Machleidt, and Nosyk [Phys. Rev. C 96, 024004 (2017)] and by Piarulli et al. [Phys. Rev. C 94, 054007 (2016)], using different $\ensuremath{\chi}\mathrm{EFT}$ formulations. In the $A=3$ calculations, (chiral) three-nucleon interactions are also accounted for. The model dependence resulting from these different formulations of the interactions is found to be mild for momentum transfer below $\ensuremath{\approx}0.8$ $\mathrm{GeV}/c$. An analysis of the convergence of the chiral expansion is also provided.