Excluded-volume model for quarkyonic matter II: Three-flavor shell-like distribution of baryons in phase space

TL;DR

This paper extends the quarkyonic matter model to include strange particles, revealing a shell-like baryon distribution in phase space and implications for neutron star properties such as mass and sound speed.

Contribution

It introduces a three-flavor extension of the excluded-volume quarkyonic model, demonstrating shell-like baryon distributions and their effects on neutron star equations of state.

Findings

Supports neutron stars with twice solar mass

Predicts high sound speed in dense matter

Shows shell-like baryon distribution in phase space

Abstract

We extend the excluded-volume model of isospin symmetric two-flavor dense quarkyonic matter [Phys. Rev. C 101, 035201 (2020)] including strange particles and address its implications for neutron stars. The effective sizes of baryons are defined from the diverging hard-core potentials in the short interdistance regime. Around the hard-core density, the repulsive core between baryons at short distances leads to a saturation in the number density of baryons and generates perturbative quarks from the lower phase space, which leads to the shell-like distribution of baryons by the Pauli exclusion principle. The strange-quark Fermi sea always appears at high densities but the $\Lambda$ hyperon shell only appears when the effective size of the $\Lambda$ hyperon is smaller than the effective size of nucleons. We find that the pressure of strange quarkyonic matter can be large enough to support neutron stars with two times solar mass and can have a large sound speed, $c_s^2 \simeq 0.7$. The fraction of the baryon number carried by perturbative quarks is about 30% at the inner core of most massive neutron stars.