Confronting the nucleonic hypothesis with current neutron star observations from GW170817 and PSR J0740+6620

Abstract: The nuclear matter equation of state is relatively well constrained at sub-saturation densities thanks to the knowledge from nuclear physics. However, studying its behavior at supra-saturation densities is a challenging task. Fortunately, the extraordinary progress recently made in observations of neutron stars and neutron star mergers has provided us with unique opportunities to unfold the properties of dense matter. Under the assumption that nucleons are the only constituents of neutron star cores, we perform a Bayesian inference using the so-called meta-modeling technique with a nuclear-physics-informed prior. The latest information from the GW170817 event by the LIGO-Virgo Collaboration (LVC) and from the radius measurement of the heaviest known neutron star PSR J0740+6620 by the Neutron Star Interior Composition Explorer (NICER) telescope and X-ray Multi-Mirror (XMM-Newton) are taken into account as likelihoods in the analysis. The impacts of different constraints on the equation of state as well as on the predictions of neutron star properties are discussed. The obtained posterior reveals that all the current observations are fully compatible with the nucleonic hypothesis. Strong disagreements between our results with future data can be identified as a signal for the existence of exotic degrees of freedom.