Hybrid neutron stars with the field correlator method

Abstract

Abstract. We study the quark deconfinement phase transition in cold (T = 0) neutron star matter and we calculate various structural properties of hybrid stars. For the quark phase, we use an equation of state (EOS) based on the Field Correlator Method (FCM) extended to the case of nonzero baryon density. For the confined hadronic phase we use a relativistic mean field model considering both pure nucleonic and hyperonic matter. We constrain the values of the gluon condensate G2, which is one of the EOS parameter within the FCM, making use of the measured mass, M = 1.97 ± 0.04 M , of the neutron star in PSR J1614-2230. Our results show that the values of G2 extracted from the mass measurement of PSR J1614-2230 are consistent with the values of the same quantity derived, within the FCM, from recent lattice QCD calculations of the deconfinement transition temperature at zero baryon chemical potential. IntroductionNeutron stars are the densest macroscopic objects in the universe. A large variety of calculations of neutron star structures [1, 2, 3, 4] predict a maximum stellar central density (the one for the maximum mass star configuration) in the range of 4 − 8 times the saturation density (∼ 2.8 × 10 14 g/cm 3 ) of nuclear matter. Therefore, neutron stars, can be viewed as natural laboratories to explore the low temperature T and high baryon chemical potential region of the phase diagram of quantum chromodynamics (QCD) [5,6]. Under these conditions nonperturbative aspects of QCD are expected to play an essential role, and a transition to a phase with deconfined quarks and gluon is expected to occur and to effect a number of interesting astrophysical phenomena [7,8,9,10,11,12,13,14,15].Current high-precision numerical calculations of QCD on a space-time lattice at zero baryon chemical potential μ b (zero baryon density) seem to indicate that at high temperature and for physical values of the quark masses, the transition to quark gluon plasma is a crossover [16] rather than a real phase transition.Unluckily, present lattice QCD calculations at finite baryon chemical potential are plagued with the so called "sign problem", which makes them unrealizable by all presently known lattice methods. Thus, in order to explore the QCD phase diagram at low temperature T and high μ b , it is necessary to adopt some approximations in QCD or to apply some QCD effective model.Along these lines the MIT bag model [17] and the Nambu Jona-Lasinio (NJL) model [18] have been widely used to calculate the quark matter EOS. However the MIT bag and the NJL

On the anomalous mass defect of strange stars in the Field Correlator Method

“…Previous investigations showed that the FCM provides new possibilities for the investigation of compact stellar configurations [31][32][33][35][36][37][38]. In the present work, we considered the general aspects of the mass defects of strange stars within the FCM without magnetic field, with special emphasis on the anomalous mass defects.…”

“…The authors of Ref. [35][36][37] also applied the FCM to the study of phase transitions in neutron stars matter and to the investigation of the structural properties and stability of hybrid stars.…”