# A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length

## TL;DR

This paper introduces a Skyrme-type functional inspired by Lee-Yang expansion, using a density-dependent neutron-neutron scattering length to accurately model neutron and symmetric matter across various densities.

## Contribution

It presents a novel functional with a density-dependent scattering length that satisfies low-density constraints and improves equation of state predictions for neutron and symmetric matter.

## Key findings

- Accurately models neutron matter from low to high densities.
- Provides good equation of state for symmetric nuclear matter.
- Satisfies low-density scattering constraints at all densities.

## Abstract

Inspired by the low--density Lee-Yang expansion for the energy of a dilute Fermi gas of density $\rho$ and momentum $k_F$, we introduce here a Skyrme--type functional that contains only $s$-wave terms and provides, at the mean--field level, (i) a satisfactory equation of state for neutron matter from extremely low densities up to densities close to the equilibrium point, and (ii) a good--quality equation of state for symmetric matter at density scales around the saturation point. This is achieved by using a density--dependent neutron-neutron scattering length $a(\rho$) which satisfies the low--density limit (for Fermi momenta going to zero) and has a density dependence tuned in such a way that the low--density constraint $|a(\rho) k_F| \le 1$ is satisfied at all density scales.