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 $\rho =0.003\hspace{0.5em}{\text{fm}}^{-3}$. The critical temperature $T_c$ 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 $A(\mathbf{p},\omega )$ 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 $\Delta$. Large values of $\Delta /T_c$ indicate that the system is not a BCS-type superfluid at low temperatures.

• Received 6 December 2009

DOI:https://doi.org/10.1103/PhysRevC.83.012801