Neutron-deuteron system and the photon polarization parameter at thermal neutron energies

Abstract

Effective field theory (EFT) is the unique, model independent and systematic low-energy version of QCD for processes involving momenta below the pion mass. A low-energy photonuclear observable in three-body systems, photon polarization parameter at thermal neutron energies is calculated by using pionless EFT up to next-to-next to leading order (N$^{2}\mathrm{LO}$). In order to make a comparative study of this model, we compared our results for photon polarization parameter with the realistic Argonne ${v}_{18}$ two-nucleon and Urbana IX or Tucson-Melbourne three-nucleon interactions. Three-body currents give small but significant contributions to some of the observables in the neutron-deuteron radiative capture cross section at thermal neutron energies. In this formalism the three-nucleon forces are needed up to N$^{2}\mathrm{LO}$ for cut-off independent results. Our result converges order by order in low energy expansion and also cut-off independent at this order.