The role of strangeness and isospin in low density expansions of hadronic matter

TL;DR

This study compares relativistic mean field models with low density expansions to assess their convergence and validity in describing hadronic matter, revealing slow convergence and differing roles of strangeness and isospin.

Contribution

It extends previous low density expansions to higher order, showing their limited convergence and analyzing the distinct impacts of strangeness and isospin in hadronic matter.

Findings

Slow convergence of the expansion due to density-dependent Dirac mass.

Non-relativistic approximation validity is questionable at subsaturation densities.

$n- ext{Lambda}$ matter is better described by low density expansions than $n-p$ matter.

Abstract

We compare relativistic mean field models with their low density expansion counterparts used to mimic non-relativistic models by consistently expanding the baryonic scalar density in powers of the baryonic number density up to ${\cal O}(13/3)$, which goes two orders beyond the order considered in previous works. We show that, due to the non-trivial density dependence of the Dirac mass, the convergence of the expansion is very slow, and the validity of the non-relativistic approximation {\bf is} questionable even at subsaturation densities. In order to analyze the roles played by strangeness and isospin we consider $n-\Lambda$ and $n-p$ matter separately. Our results indicate that these degrees of freedom play quite different roles in the expansion mechanism and $n-\Lambda$ matter can be better described by low density expansions than $n-p$ matter in general.