New class of hybrid EoS and Bayesian M-R data analysis

TL;DR

This paper introduces a new class of hybrid equations of state for neutron stars, incorporating features like quark exchange effects and multiquark interactions, and uses Bayesian analysis to identify observable signatures of phase transitions.

Contribution

It develops a systematic framework for hybrid star EoS with strong first order phase transitions and demonstrates how high-mass twin stars can be used to distinguish these models.

Findings

Hybrid EoS can produce various mass-radius patterns including high-mass twins.

Observation of twin stars can strongly favor models with a strong first order phase transition.

Bayesian analysis shows potential to discriminate between different EoS based on star observations.

Abstract

We explore systematically a new class of two-phase equations of state (EoS) for hybrid stars that is characterized by three main features : (1) stiffening of the nuclear EoS at supersaturation densities due to quark exchange effects (Pauli blocking) between hadrons, modelled by an excluded volume correction, (2) stiffening of the quark matter EoS at high densities due to multiquark interactions and (3) possibility for a strong first order phase transition with an early onset and large density jump. The third feature results from a Maxwell construction for the possible transition from the nuclear to a quark matter phase and its properties depend on the two parameters used for (1) and (2), respectively. Varying these two parameters one obtains a class of hybrid EoS that yields solutions of the Tolman-Oppenheimer-Volkoff (TOV) equations for sequences of hadronic and hybrid stars in the mass-radius diagram which cover the full range of patterns according to the Alford-Han-Prakash classification following which a hybrid star branch can be either absent, connected or disconnected with the hadronic one. The latter case often includes a tiny connected branch. The disconnected hybrid star branch, also called "third family", corresponds to high-mass twin stars characterized by the same gravitational mass but different radii. We perform a Bayesian analysis and demonstrate that the observation of such a pair of high-mass twin stars would have a sufficient discriminating power to favor hybrid EoS with a strong first order phase transition over alternative EoS.