Pairing in high-density neutron matter including short- and long-range correlations

TL;DR

This study investigates how short- and long-range correlations affect the superfluid pairing gap in high-density neutron matter, revealing that correlations suppress but do not eliminate the gap, with implications for neutron star cooling.

Contribution

It introduces a comprehensive approach including both short- and long-range correlations in the pairing gap calculation for neutron matter, a novel combination in this context.

Findings

Short-range correlations strongly suppress the pairing gap.

Long-range correlations slightly increase the gap when SRC are included.

Maximum gaps are around 0.1 to 0.2 MeV, weakly dependent on interaction hardness.

Abstract

The influence of short-range correlations (SRC) on the spectral distribution of neutrons is incorporated in the solution of the gap equation for the ${}^3P_2-{}^3F_2$ coupled channel in pure neutron matter at high density. This effect is studied for three different realistic interactions. The gap in this channel is strongly suppressed by these correlations but does not vanish. For a consistent treatment we also include for the first time the effect of long-range correlations (LRC) by incorporating polarization terms in addition to the bare interaction. This allows the neutrons to exchange density and spin fluctuations governed by the strength of Landau parameters with values that are consistent with the available literature. While these LRC have an antiscreening tendency, they only slightly increase the gap in the ${}^3P_2-{}^3F_2$ coupled channel for all three realistic interactions as long as SRC are included. All three interactions generate maximum gaps around 0.1 to 0.2 MeV at most with a small dependence on the hardness of the interaction. These results are relevant for the cooling scenarios of neutron stars, in particular the young neutron star in Cassiopeia A.