Quantum Monte Carlo study of dilute neutron matter at finite temperatures

We report results of fully nonperturbative, path integral Monte Carlo calculations for dilute neutron matter. The neutron-neutron interaction in the s channel is parameterized by the scattering length and the effective range. We calculate the energy and the chemical potential as a function of temperature at density ρ=0.003 fm^-3. The critical temperature Tc for the superfluid-normal phase transition is estimated from the finite size scaling of the condensate fraction. At low temperatures we extract the spectral weight function A(p,ω) from the imaginary time propagator using the methods of maximum entropy and singular value decomposition. We determine the quasiparticle spectrum, which can be accurately parameterized by three parameters: an effective mass m*, a mean-field potential U, and a gap Δ. Large values of Δ/Tc indicate that the system is not a BCS-type superfluid at low temperatures.