Photon linear polarization coefficient of the radiative capture process ²H(p, γ)³He at thermal energies

The photon polarization parameter of the proton-deuteron radiative capture process at thermal proton energies is calculated up to leading order (LO), using pionless effective field theory (EFT). In order to make a comparative study of this model, we compare our results for the photon polarization parameter with the realistic Argonne _v14(AV14) and Argonne _v18(AV18) modern nucleon-nucleon potentials and Urbana IX or Tucson-Melbourne three-nucleon interactions. The theoretical description of the ²H(p, γ)³He reaction at thermal energies is complicated by the presence of the Coulomb interaction. Only the s-wave capture contribution to the thermal energy of this reaction is calculated. Three-body currents give small but significant contributions to some of the observables in the proton-deuteron radiative capture cross section at thermal neutron energies. Our result is in good agreement with the available experimental data and potential models' calculation at this order. (authors)