Holographic QCD in the NICER era

TL;DR

This paper combines gauge/gravity duality and ab initio methods to model neutron stars, finding they are likely fully hadronic without quark cores, and aligns well with recent NICER measurements.

Contribution

It introduces hybrid equations of state integrating duality and ab initio approaches, providing new insights into neutron star composition and constraints from recent observations.

Findings

Neutron stars are likely fully hadronic without quark matter cores.

NICER measurements impose mild constraints on the hybrid equations of state.

Adding mass bounds from GW170817 tightens the model constraints.

Abstract

We analyze families of hybrid equations of state of cold QCD matter, which combine input from gauge/gravity duality and from various ab initio methods for nuclear matter at low density, and predict that all neutron stars are fully hadronic without quark matter cores. We focus on constraints from recent measurements by the NICER telescope on the radius and mass of the millisecond pulsar PSR J0740+6620. These results are found to be consistent with our approach: they set only mild constraints on the hybrid equations of state, and favor the most natural models which are relatively stiff at low density. Adding an upper bound on the maximal mass of neutron stars, as suggested by the analysis of the GW170817 neutron star merger event, tightens the constraints considerably. We discuss updated predictions on observables such as the transition density and latent heat of the nuclear to quark matter transition as well as the masses, radii, and tidal deformabilities of neutron stars.