Excluded volume effects in the hybrid star EoS

TL;DR

This paper introduces a new two-phase model for the hybrid equation of state of quark-nuclear matter, incorporating excluded volume effects in both phases, which significantly influence the properties of hybrid stars.

Contribution

It presents a novel 2-phase hybrid EoS model that accounts for phase space occupation effects in hadronic and quark matter, impacting deconfinement transition and star properties.

Findings

Mass-radius relations satisfy the 2 solar mass constraint.

High-mass twin star phenomenon is reproduced.

Excluded volume effects are crucial for star modeling.

Abstract

In this contribution, we outline a new 2-phase description of the quark-nuclear matter hybrid equation of state that takes into account effects of phase space occupation (excluded volume) in both, the hadronic and the quark matter phases. For the nuclear matter phase, the reduction of the available volume at increasing density leads to a stiffening, while for the quark matter phase a reduction of the effective string tension in the confining density functional is obtained. The deconfinement phase transition in the resulting hybrid equation of state is sensitive to both excluded volume effects. As an application, we consider matter under compact star constraints of electric neutrality and $\beta$-equilibrium. We obtain mass-radius relations for hybrid stars that fulfill the $2M_\odot$ constraint and exhibit the high-mass twin phenomenon. Both features depend sensitively on the excluded volume.