Hadron resonance gas with density-dependent interactions for neutron stars and heavy-ion collisions

Abstract

We present a density-dependent generalization of the van der Waals hadron resonance gas model (DD-HRG) for describing both the hot hadronic matter created in heavy-ion collisions and the cold, dense matter inside neutron stars. Non-resonant interactions are incorporated through a generalized excluded-volume prescription with a density-dependent available-volume fraction, supplemented by an arbitrary density-dependent mean field. With isospin-dependent interaction parameters constrained by empirical properties of nuclear matter, the resulting equation of state extends the causality range to include neutron-star interiors and supports two-solar-mass stars. It also improves the description of lattice QCD thermodynamics and conserved-charge susceptibilities at vanishing baryochemical potential, with lattice data favoring reduced repulsion among strange baryons. This DD-HRG framework is available within the latest version of the open-source Thermal-FIST package.

Comments: 4 pages, 3 figures, contribution to the proceedings of SQM 2026