Many-body approximations to the superfluid gap and critical temperature in pure neutron matter

TL;DR

This paper investigates how many-body effects influence superfluid pairing gaps and critical temperatures in pure neutron matter, revealing deviations from BCS theory and aligning with experimental and unitary Fermi gas data.

Contribution

It introduces advanced many-body approximations that account for short-range correlations, providing new insights into neutron matter superfluidity beyond standard BCS predictions.

Findings

Medium effects reduce pairing gaps and critical temperatures.

The gap to critical temperature ratio is constant in mean-field approximation.

In low-density regimes, the ratio exceeds BCS predictions and aligns with experiments.

Abstract

We compute singlet pairing gaps and critical temperatures in pure neutron matter with different many-body approximations. Medium effects tend to reduce gaps and critical temperatures compared to the standard BCS ansatz. In the mean-field approximation, the ratio of these two quantities remains constant across a wide range of densities. This constant ratio is close to the universal prediction of BCS theory, whether three-neutron interactions are included or not. Using a more sophisticated many-body approach that incorporates the effect of short-range correlations in pairing properties, we find that the gap to critical temperature ratio in the low-density regime is substantially larger than the BCS prediction, independently of the interaction. In this region, our results are relatively close to experiments and theoretical calculations from the unitary Fermi gas. We also find evidence for a different density dependence of zero-temperature gaps and critical temperatures in neutron matter.