Delta baryons and diquark formation in the cores of neutron stars

GERMÁN MALFATTI; MILVA G. ORSARIA; IGNACIO FRANCISCO RANEA SANDOVAL; GUSTAVO A. CONTRERA; FRIDOLIN WEBER

PHYSICAL REVIEW D - PARTICLE AND FILDS

American Physical Society

Año: 2020

0556-2821

We investigate the hadron-quark phase transition in cold neutron stars in light of (i) the observed limits on the maximum-mass of heavy pulsars, (ii) constraints on the tidal properties inferred from the gravitational waves emitted in binary neutron-star mergers, and (iii) mass and radius constraints derived from the observation of hot spots on neutron star observed with NICER. Special attention is directed to the possible presence of ∆(1232) baryons in neutron star matter. Our results indicate that this particle could make up a large fraction of the baryons in neutron stars and thus havea significant effect on the properties of such objects, particularly on their radii. This is partially caused by the low density appearance of ∆s for a wide range of theoretically defensible sets of meson?hyperon, SU(3) ESC08 model, and meson?∆ coupling constants. The transition of hadronic matterto quark matter, treated in the 2SC+s condensation phase, is found to occur only in neutron stars very close to the mass peak. Nevertheless, quark matter may still constitute an appreciable fractionof the stars? total matter if the phase transition is treated as Maxwell-like (sharp), in which case the neutron stars located beyond the gravitational mass peak would remain stable against gravitational collapse. In this case, the instability against gravitational collapse is shifted to a new (terminal) mass different from the maximum-mass of the stellar sequence, giving rise to stable compact objects with the same gravitational masses as those of the neutron stars on the traditional branch, but whose radii are smaller by up to 1 km. All models for the equation of state of our study fall comfortably within the bound established very recently by Annala et al. (Nature Physics, 2020)