# ${\it Ab~initio}$ constraints on thermal effects of the nuclear equation of state

## TL;DR

This paper uses ab initio many-body calculations to analyze the thermal properties of nuclear matter, revealing the density and temperature dependence of the thermal index crucial for astrophysical models.

## Contribution

It provides the first ab initio analysis of the thermal index's density and temperature dependence, highlighting the importance of many-body forces in nuclear matter.

## Key findings

- Thermal index varies with density and temperature.
- Many-body forces significantly influence the thermal index.
- Constant thermal index assumptions may be invalid for neutron-star mergers.

## Abstract

We exploit the many-body self-consistent Green's function method to analyze finite-temperature properties of infinite nuclear matter and to explore the behavior of the thermal index used to simulate thermal effects in equations of state for astrophysical applications. We show how the thermal index is both density and temperature dependent, unlike often considered, and we provide an error estimate based on our ${\it ab~initio}$ calculations. The inclusion of many-body forces is found to be critical for the density dependence of the thermal index. We also compare our results to a parametrization in terms of the density dependence of the nucleon effective mass. Our study questions the validity of predictions made for the gravitational-wave signal from neutron-star merger simulations with a constant thermal index.