Speed of sound bounds and first-order phase transitions in compact stars

TL;DR

This paper investigates how different theoretical bounds on the speed of sound influence the modeling of phase transitions in compact stars, using hybrid models constrained by recent astronomical data.

Contribution

It introduces a systematic analysis of speed of sound bounds in hybrid star models, comparing abrupt and smooth phase transition schemes with implications for stellar stability.

Findings

Speed of sound bounds significantly affect the parameter space of phase transitions.

Hybrid models with different bounds show varied stability and transition characteristics.

The study highlights potential thermodynamic inconsistencies at high densities.

Abstract

In the present study, we employ three distinct, physically motivated speed of sound bounds to construct hybrid models, where the high-density phase is described by the maximally stiff equation of state. In particular, we consider the bounds related to special relativity, relativistic kinetic theory and conformality. The low-density hadronic phase is described by a state-of-the-art microscopic relativistic Brueckner-Hartree-Fock theory. This work aims to access the effect of the different speed of sound constraints on the relevant parameter space of the key parameters of first-order phase transitions by utilizing recent astronomical data. This involves a systematic analysis that also includes two distinct schemes for the construction of hybrid models (abrupt and smooth). Finally, a relevant discussion is conducted on the possible occurrence of a thermodynamic inconsistency that is related to the stability of the high-density phase over hadronic matter at large densities.