The Constant-Sound-Speed parameterization for NJL models of quark matter in hybrid stars

IGNACIO F. RANEA-SANDOVAL; GUSTAVO A. CONTRERA; SOPHIA HAN; FRIDOLIN WEBER; MILVA G. ORSARIA; MARK G. ALFORD

PHYS. REV. - C

AMER PHYSICAL SOC

Lugar: New York; Año: 2016 vol. 93 p. 1 - 12

0556-2813

The discovery of pulsars as heavy as 2 solar masses has led astrophysicists to rethink the corecompositions of neutron stars, ruling out many models for the nuclear equations of state (EoS).We explore the hybrid stars that occur when hadronic matter is treated in a relativistic mean-field approximation and quark matter is modeled by three-flavor local and non-local Nambu−Jona-Lasinio (NJL) models with repulsive vector interactions. The NJL models typically yield equationsof state that feature a first-order transition to quark matter. Assuming that the quark-hadronsurface tension is high enough to disfavour mixed phases, and restricting to EoSs that allow startsto reach 2 solar masses, we find that the appearance of the quark matter core either destabilizesthe star immediately (this is typical for non-local NJL models) or leads to a very short hybrid starbranch in the mass-radius relation (this is typical for local NJL models). Using the Constant-Sound-Speed parametrization we can see that the reason for the near-absence of hybrid stars is that thetransition pressure is fairly high and the transition is strongly first-order.