Finite-size effects on the hadron-quark phase transition in neutron stars

TL;DR

This paper investigates how finite-size effects like surface and Coulomb energies influence the hadron-quark phase transition in neutron stars, showing they can significantly alter the mixed phase region and star properties.

Contribution

It introduces a method to incorporate finite-size effects into the phase transition conditions, providing more accurate models of neutron star interiors.

Findings

Finite-size effects reduce the mixed phase region.

Massive stars can have a mixed-phase core.

Vector interactions stiffen the quark matter equation of state.

Abstract

We study the finite-size effects, like the surface and Coulomb energies, on the hadron-quark mixed phase in neutron stars. The equilibrium conditions for coexisting hadronic and quark phases are derived by minimizing the total energy including the surface and Coulomb contributions, which are different from the Gibbs conditions without finite-size effects. We employ the relativistic mean-field model to describe the hadronic phase, while the Nambu-Jona-Lasinio model with vector interactions is used for the quark phase. It is found that finite-size effects can significantly reduce the region of the mixed phase, and the results lie between those of the Gibbs and Maxwell constructions. We show that a massive star may contain a mixed-phase core and its size depends on the surface tension of the hadron-quark interface and the vector coupling between quarks. The repulsive vector interaction in the Nambu-Jona-Lasinio model can stiffen the equation of state of quark matter, and therefore, delay the phase transition and increase the maximum mass of neutron stars.