Developments in Chiral effective Field Theory for Nuclear Matter

TL;DR

This paper reviews a systematic chiral effective field theory approach for nuclear matter, calculating energy densities and neutron star properties, and providing bounds on gravitational constants in strong fields.

Contribution

It introduces a chiral power counting scheme for in-medium chiral perturbation theory and applies it to calculate nuclear matter properties and neutron star constraints.

Findings

Good agreement with many-body calculations for energy density

Upper mass limit for neutron stars around 2.3 solar masses

Constraints on gravitational constant in strong fields

Abstract

We review on a chiral power counting scheme for in-medium chiral perturbation theory with nucleons and pions as degrees of freedom \cite{ref}. It allows for a systematic expansion taking into account local as well as pion-mediated inter-nucleon interactions. Based on this power counting, one can identify classes of non-perturbative diagrams that require a resummation. We then calculate the nuclear matter energy density for the symmetric and purely neutron matter cases up-to-and-including next-to-leading order (NLO), in good agreement with sophisticated many-body calculations. Next, the neutron matter equation of state is applied to calculate the upper limit for neutron stars, with an upper bound around 2.3 solar masses, large enough to accommodate the most massive neutron star observed until now. We also apply our equation state to constraint $G_N$ in exceptionally large gravitational fields.