# Tetraneutron condensation in neutron rich matter

## TL;DR

This paper explores the potential formation of tetraneutron resonant states in neutron-rich matter within neutron stars, analyzing their impact on nuclear composition and pairing properties using a relativistic density functional model.

## Contribution

It introduces a relativistic density functional approach to study tetraneutron condensation in neutron star matter, considering multiple hadronic species and mesonic interactions.

## Key findings

- Tetraneutrons may form in outer neutron star crusts at certain densities.
- Their presence can significantly alter nucleon pairing fractions.
- Tetraneutrons can carry a substantial portion of baryonic charge.

## Abstract

In this work we investigate the possible condensation of tetraneutron resonant states in the lower density neutron rich gas regions inside Neutron Stars (NSs). Using a relativistic density functional approach we characterize the system containing different hadronic species including, besides tetraneutrons, nucleons and a set of light clusters ($^3$He, $\alpha$ particles, deuterium and tritium). $\sigma,\omega$ and $\rho$ mesonic fields provide the interaction in the nuclear system. We study how the tetraneutron presence could significantly impact the nucleon pairing fractions and the distribution of baryonic charge among species. For this we assume that they can be thermodynamically produced in an equilibrated medium and scan a range of coupling strengths to the mesonic fields from prescriptions based on isospin symmetry arguments. We find that tetraneutrons may appear over a range of densities belonging to the outer NS crust carrying a sizable amount of baryonic charge thus depleting the nucleon pairing fractions.