Impact of massive neutron star radii on the nature of phase transitions in dense matter

TL;DR

This paper investigates how large neutron star radii influence the nature of phase transitions in dense matter, challenging conventional views by constructing stiffer equations of state with first-order phase transitions.

Contribution

It presents explicit models of stiff equations of state with first-order phase transitions, contrasting with traditional expectations, and compares them with quarkyonic matter models.

Findings

First-order phase transitions can occur in stiffer EoSs than previously thought.

Stiff EoSs with phase transitions can mimic quarkyonic matter properties.

Large neutron star radii do not necessarily imply softer equations of state.

Abstract

The last few years have seen tremendous progress in the observation of the global properties of neutron stars (NSs), e.g. masses, radii and tidal deformabilities. Such properties provide information about possible phase transitions in the inner cores of NSs, provided the connection between observed masses and radii and the equation of state (EoS) is well understood. We focus the present study on first-order phase transitions, which often softens the EoS and consequently reduces the maximum mass as well as the radii of NSs. Here, we challenge this conventional expectation by constructing explicit examples of EoSs undergoing a first-order phase transition, but which are much stiffer that their purely hadronic counterparts. We also provide comparisons with the recently proposed quarkyonic EoS which suggests a strong repulsion in the core of NSs, and we show that their stiffness can be realistically masqueraded by first-order phase transitions to exotic matter.