Exceeding the conformal limit inside rotating neutron stars: Implications to modified theories of gravity

TL;DR

This paper explores how rapid rotation affects the superconformal properties of neutron stars and their potential to test scalar-tensor theories of gravity, especially in the context of the averaged speed of sound exceeding the conformal limit.

Contribution

It investigates the impact of rapid rotation on the superconformal limit inside neutron stars and its implications for testing modified theories of gravity, particularly scalar-tensor models.

Findings

Rotation influences the superconformal property of neutron stars.

Superconformal conditions can serve as tests for scalar-tensor gravity theories.

Neutron stars may exceed the conformal limit under certain conditions.

Abstract

At the supranuclear densities achieved inside a neutron star, matter may exhibit extreme properties. In particular, it may be the case that a suitable average of the speed of sound squared exceeds the so-called conformal limit, i.e., $\langle c_s^2 \rangle > 1/3$, a condition that is equivalent to the positiveness of the trace of the energy-momentum tensor at the stellar center. This property, that holds for highly compact neutron stars obeying many (but not any) realistic equations of state, would turn these objects into interesting laboratories for tests of several scalar extensions of general relativity. In this paper, we investigate how rapid rotation influences the superconformality of the averaged speed of sound squared and modified gravity effects that depend thereupon, paying particular attention to scalar-tensor theories prone to the spontaneous scalarization effect.