Hybrid Stars in the Light of the Massive Pulsar PSR J1614–2230

Abstract

We perform a systematic study of hybrid star configurations using several parametrizations of a relativistic mean-field hadronic EoS and the NJL model for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and TM1 parametrizations, as well as the very stiff NL3 model. In the NJL Lagrangian we include scalar, vector and 't Hooft interactions. The vector coupling constant g v is treated as a free parameter. We also consider that there is a split between the deconfinement and the chiral phase transitions which is controlled by changing the conventional value of the vacuum pressure −Ω 0 in the NJL thermodynamic potential by −(Ω 0 + δΩ 0 ), being δΩ 0 a free parameter. We find that, as we increase the value of δΩ 0 , hybrid stars have a larger maximum mass but are less stable, i.e. hybrid configurations are stable within a smaller range of central densities. For large enough δΩ 0 , stable hybrid configurations are not possible at all. The effect of increasing the coupling constant g v is very similar. We show that stable hybrid configurations with a maximum mass larger than the observed mass of the pulsar PSR J1614-2230 are possible for a large region of the parameter space of g v and δΩ 0 provided the hadronic equation of state contains nucleons only. When the baryon octet is included in the hadronic phase, only a very small region of the parameter space allows to explain the mass of PSR J1614-2230. We compare our results with previous calculations of hybrid stars within the NJL model. We show that it is possible to obtain stable hybrid configurations also in the case δΩ 0 = 0 that corresponds to the conventional NJL model for which the pressure and density vanish at zero temperature and chemical potential. Subject headings: stars: neutron -equation of state -PSR

Dynamical generation of a repulsive vector contribution to the quark pressure

“…(5.5) suggests that another possibility is that higher order contributions may produce a contribution with a positive sign so that eventually c 2 will converge to the SB limit. Within this scenario it appears that the (rather quick) convergence of the LN result for c 2 towards the SB could be accidental 3 . As already emphasized, at order-δ 2 the OPT considers three different topologies, including vertex corrections, which would belong to the NLO and NNLO in a 1/N c expansion.…”

Maximum mass of a hybrid star having a mixed-phase region based on constraints set by the pulsar PSR J1614-2230

“…This maximum mass limit is for this hadronic and quark matter EOSs. Stiffer EOS sets (like hadronic NL3 and quark quark NJL model) for the mixed hybrid star can produce much higher maximum mass [37]. From the figure it is also clear that the maximum mass of the star corresponds to a radius of about 10km.…”

“…For the mass to reach the maximum mass limit they showed that the crossover has to take place at low density and the quark matter has to be strongly interact-ing. Using very stiff EOS sets (hadronic NL3 and quark quark NJL model) the maximum mass limit for the hybrid star can be raised much higher as shown by Lenzi & Lugones [37].…”

Crystalline chiral condensates as a component of compact stars

“…In this sense, the transition occurring at µ tr should be interpreted as a "deconfinement" phase transition, which is not built from fundamental gluon dynamics, but only as an effective construction relying on the two phenomenological models involved. While a proper inclusion of confinement properties and the interplay between chiral and deconfinement phase transitions is clearly beyond the scope of this paper, in the spirit of previous works [11,49] we attempt to incorporate these effects in a crude way through the introduction of a constant shift to the NJL vacuum pressure δΩ 0 , which will be treated as a free parameter.…”