Kinetic theory and the speed of sound in dense matter

Abstract

We discuss a constraint on the speed of sound, $c_s^2$, derived from relativistic kinetic theory and show how it can be expressed in terms of the average sound speed, $⟨c_s^2⟩$. This reformulation highlights the interplay between instantaneous and integrated stiffness of the equation of state and allows the kinetic-theory bound to be visualized as a restriction in the $c_s^2$-$⟨c_s^2⟩$ plane.

Comments: proceedings of The 29th International Nuclear Physics Conference (INPC 2025), Daejeon, Korea, 25-30 May, 2025