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Hybrid star properties with the NJL and mean field approximation of QCD models: A Bayesian approach

Authors: Milena Albino, Tuhin Malik, Márcio Ferreira, Constança Providência

Ref.: Phys.Rev.D 110, 083037 (2024)

Abstract: The composition of the core of neutron stars (NSs) is still under debate. One possibility is that because of the high densities reached in their cores, matter could be deconfined into quark matter. In this work, we investigate the possible existence of hybrid stars, using microscopic models to describe the different phases of matter. Within the adopted microscopic models we aim at calculating both the properties of NSs and the properties of matter. In particular, we want to probe the influence of perturbative quantum chromodynamics (pQCD) calculations and analyze the properties that identify a transition to deconfined matter. A Bayesian approach using a Markov-Chain Monte Carlo sampling process is applied to generate eight sets of equations of state. A Maxwell construction is adopted to describe the deconfinement transition. For the hadronic phase, we consider a stiff and a soft equations of state (EOS) obtained from the relativistic mean field model with nonlinear meson terms. For the quark phase, we use two different models: the Nambu-Jona-Lasinio model with multiquark interactions and the mean field theory of QCD, a model similar to the MIT bag model with a vector term. Bayesian inference was applied to determine the model parameters that satisfy the x-ray observations from NICER and have phase transition at densities between 0.15 and 0.40  fm−3. We have also applied restrictions from the pQCD calculations to half of the sets. Hybrid stars are compatible with current observational data. The restrictions of pQCD reduce the value of the maximum mass. However, even when applying this restriction, the models were able to reach values of 𝑀max=2.1–2.3⁢𝑀⊙. The conformal limit was still not attained at the center of the most massive stars. The vector interactions are essential to describe hybrid stars with a mass above 2⁢𝑀⊙. The multiquark interactions introduced may affect the limits of some quantities considered as indicators of the presence of a deconfined phase. It is possible to find a set of EOS, that predict that inside NSs the renormalized matter trace anomaly is always positive.

DOI: 10.1103/PhysRevD.110.083037

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