Speaker
Description
Compact stars provide unique astrophysical laboratories for exploring the properties of dense nuclear matter. Observations of pulsars, together with recent gravitational-wave detections, have placed stringent constraints on the nuclear equation of state (EOS). Among various thermodynamic quantities, the speed of sound plays a central role in understanding the structure of neutron star and the behavior of matter at supranuclear densities.
In this work, we present a detailed investigation of the thermodynamic structure of the speed of sound and its decomposition in dense matter. We demonstrate that the curvature term of the speed of sound undergoes a sign change in purely hadronic EOSs, even in the absence of a phase transition or the system reaching the conformal limit. This behavior is directly connected to the maximum of the first derivative of the energy per particle. We further analyze the behavior of the trace anomaly and the polytropic index within the relativistic mean-field (RMF) framework, showing that the sign of the trace anomaly at high densities is sensitive to whether the EOS is stiff or soft.
We also investigate hadron–quark phase transitions using both Maxwell and Gibbs constructions and apply the speed-of-sound decomposition scheme to these scenarios. In particular, we explore the behavior of the average speed of sound in purely hadronic stars, quark stars, and hybrid stars, identifying characteristic signatures associated with the presence of a phase transition. Finally, we extend our analysis to finite-temperature phase transitions, highlighting their impact on the thermodynamic properties of dense matter.
