Neutron matter from low-momentum interactions

We present a perturbative calculation of the neutron matter equation of state based on low-momentum two- and three-nucleon interactions. Our results are compared to the model-independent virial equation of state and to variational calculations, and we provide theoretical error estimates by varying the cutoff used to regulate nuclear interactions. In addition, we study the dependence of the BCS $^1$S$_0$ superfluid pairing gap on nuclear interactions and on the cutoff. The resulting gaps are well constrained by the nucleon-nucleon scattering phase shifts, and the cutoff dependence is very weak for sharp or sufficiently narrow smooth regulators with cutoffs $\lm > 1.6 \fmi$.