Characterizing the quark-hadron mixed phase in compact star cores : sensitivity to nuclear saturation and quark-model parameters at finite-temperature

TL;DR

This study investigates how finite temperature and nuclear and quark matter parameters influence the quark-hadron phase transition in neutron star cores, affecting the star's structure and observable properties.

Contribution

It systematically analyzes the impact of nuclear saturation properties and quark model parameters on the mixed phase and star characteristics at finite temperature.

Findings

Effective mass and symmetry energy mainly control the mixed phase width.

Increasing temperature reduces the mixed phase and softens the equation of state.

Variations in parameters significantly affect stellar radii and maximum mass.

Abstract

A thorough knowledge of the quark-hadron phase transition in hot and dense matter is essential for constraining the equation of state of neutron stars. In this work, we study the thermodynamics of the quark-hadron mixed phase at finite temperature using the Gibbs construction and examine its impact on hybrid star matter. We systematically explore the role of nuclear saturation properties, including the effective nucleon mass, incompressibility, symmetry energy coefficient, and its slope, together with quark matter parameters such as the bag constant and the vector coupling strength. We find that the width of the mixed phase is mainly controlled by the effective mass and symmetry energy, while the roles of incompressibility and symmetry energy slope are comparatively weak, particularly at higher temperatures. Thermal effects substantially modify the phase structure: increasing temperature reduces the mixed-phase width and softens the equation of state in the coexistence region due to Gibbs phase equilibrium constraints. These effects are reflected in the behavior of the speed of sound, the trace anomaly, and its derivative. Variations in the symmetry energy, effective mass, and quark parameters significantly affect the hadron-quark transition, stellar radii, and maximum mass, while finite temperature softens the equation of state and enhances radius jumps in the mixed phase. Strong vector repulsion is essential to reconcile massive pulsar observations with NICER constraints, whereas weaker repulsion favors more compact, low-mass configurations.