Relativistic analysis of neutron β decay at finite density

We present a fully relativistic analysis of neutron decay in a finite-density environment. For the zero-density case we derive an analytic formula for the decay rate and generalize it to finite densities. The rates are calculated from the imaginary part of the neutron self-energy, using the generalized Cutkosky rules for the real-time formulation of quantum field theory at finite temperature by Niemi and Semenoff. This method is very straightforward and elegant since it includes both decay and inverse decay modes in a nontrivial way