Average speed of sound in neutron stars

The structure of the dense-matter equation of state is essential for the phenomenology of neutron stars. In this work, we relate the thermodynamic properties to the average speed of sound in the interior of a star. We study the consequences of the restoration of conformal symmetry. In particular, we show that if the trace anomaly vanishes in the centers of maximally massive neutron stars, the speed of sound likely exceeds its conformal value and exhibits nonmonotonic behavior. We also find that the additional assumption of positive definiteness of the trace anomaly naturally induces a local peak of the speed of sound at densities realized in the cores of neutron stars. We also discuss the stability condition for the hybrid neutron stars Possible implications for the dense matter equation of state and the phenomenology of neutron stars are also discussed.