Superfluid Phase Transitions and Effects of Thermal Pairing Fluctuations in Asymmetric Nuclear Matter

We investigate superfluid phase transitions of asymmetric nuclear matter at finite temperature (T) and density (ρ) with a low proton fraction (Y(p) ≤ 0.2), which is relevant to the inner crust and outer core of neutron stars. A strong-coupling theory developed for two-component atomic Fermi gases is generalized to the four-component case, and is applied to the system of spin-1/2 neutrons and protons. The phase shifts of neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) interactions up to k = 2 fm(−1) are described by multi-rank separable potentials. We show that the critical temperature [Formula: see text] of the neutron superfluidity at Y(p) = 0 agrees well with Monte Carlo data at low densities and takes a maximum value [Formula: see text] = 1.68 MeV at [Formula: see text] with ρ(0) = 0.17 fm(−3). Also, the critical temperature [Formula: see text] of the proton superconductivity for Y(p) ≤ 0.2 is substantially suppressed at low densities due to np-pairing fluctuations, and starts to dominate over [Formula: see text] only above [Formula: see text] (0.77) for Y(p) = 0.1(0.2), and (iii) the deuteron condensation temperature [Formula: see text] is suppressed at Y(p) ≤ 0.2 due to a large mismatch of the two Fermi surfaces.