The $^1$S$_0$ pairing gap in neutron matter

TL;DR

This paper presents ab initio quantum Monte Carlo calculations of the S wave pairing gap in neutron matter, incorporating realistic interactions and finite-size effects, with implications for neutron star physics and cold atom experiments.

Contribution

It introduces a novel ab initio approach using auxiliary field diffusion Monte Carlo to accurately compute the neutron matter pairing gap, including finite-size corrections and comparison with previous studies.

Findings

Pairing gap shows modest suppression compared to mean-field BCS values.

Results are relevant for understanding neutron star cooling and cold atom experiments.

Finite-size effects are systematically studied and extrapolated to the thermodynamic limit.

Abstract

We report ab initio calculations of the S wave pairing gap in neutron matter calculated using realistic nuclear Hamiltonians that include two- and three-body interactions. We use a trial state, properly optimized to capture the essential pairing correlations, from which we extract ground state properties by means of auxiliary field diffusion Monte Carlo simulations. We extrapolate our results to the thermodynamic limit by studying the finite-size effects in the symmetry-restored projected Bardeen-Cooper-Schrieffer (PBCS) theory and compare our results to other ab initio studies done in the past. Our quantum Monte Carlo results for the pairing gap show a modest suppression with respect to the mean-field BCS values. These results can be connected to cold atom experiments, via the unitarity regime where fermionic superfluidity assumes a unified description, and they are important in the prediction of thermal properties and the cooling of neutron stars.