Effects of quark-matter symmetry energy on hadron-quark coexistence in neutron-star matter

Abstract

We examine the effects of the isovector-vector coupling and hypercharge-vector coupling in quark matter on hadron-quark coexistence in neutron-star matter. The relativistic mean field theory with the TM1 parameter set and an extended TM1 parameter set are used to describe hadronic matter, and the Nambu-Jona-Lasinio model with scalar, isoscalar-vector, isovector-vector and hyperchargevector couplings is used to describe deconfined quark matter. The hadron-quark phase transition is constructed via the Gibbs conditions for phase equilibrium. The isovector-vector and hyperchargevector couplings in quark matter enhance the symmetry energy and hypercharge symmetry energy in neutron-star matter, while their effects are found to be suppressed at high densities by the strange quarks. As a result, the hadron-quark mixed phase shrinks with only isovector-vector coupling and moves to higher density with isovector-vector and hypercharge-vector couplings. The maximum mass of neutron-star increases slightly with isovector-vector and hypercharge-vector couplings.

Hybrid stars with large strange quark cores constrained by GW170817

“…1 Each hybrid EoS consists of a hadronic phase connected to a quark phase through a first-order phase transition. This two-model approach has been widely used [26,[33][34][35][36][37]. The first-order phase transition from hadronic to quark matter is achieved imposing the Maxwell construction, in which both phases are in chemical, thermal and mechanical equilibrium:…”

“…While different procedures can be used for the matching of the two EoS [32], we consider a Maxwell construction in order to describe a first-order phase transition from hadron to quark mater. The reliability of such approach depends on the still unknown surface tension between both phases; however, it is justified and has been widely considered [26,[33][34][35][36][37], if the surface tension, σ, is of the order of σ ≳ 40 MeV fm −2 [38]. The NJL model has been explored in describing the quark phase of a hybrid EoS in several works, e.g., [27,36,39].…”

Constraint to chiral invariant masses of nucleons from GW170817 in an extended parity doublet model

“…It might be changed by e.g., including effects of quark degrees (See e.g., Refs. [26,33,[57][58][59][60][61][62][63][64]. ).…”

“…Then, although the present prediction for (m (1) 0 , m (2) 0 ) = (795, 860) MeV does not reproduce the super-heavy neutron stars with 2M mass [55,56], it will be changed by e.g., including effects of quark degrees (See e.g., Refs. [26,33,[57][58][59][60][61][62][63][64]. ).…”

Hybrid stars from a constrained equation of state

“…The quark model chosen is the well known Nambu-Jona-Lasinio (NJL) model, an e↵ective model of QCD, that considers chiral symmetry preserving interactions [9,10]. The use of the NJL model in such two-model approaches has been widely explored both considering a firstorder phase transition [11][12][13][14][15][16] and with a smooth (crossover) transition between both phases…”