Improved treatment of neutron star cooling via modified Urca Process

Most neutron stars cool predominately via the modified Urca process, in which emitted neutrinos carry away energy. The traditional treatment for the in-medium nucleon propagator in the modified Urca process uses crude approximations. We reformulate the propagator by including the nucleon self-energy and examine the effect of this new propagator on the neutrino emissivity due to the modified Urca process.