Abstract
We explore the possibility of obtaining heavy hybrid stars within the framework of the two flavor Nambu-Jona-Lasinio model that includes 8-quark interactions in the scalar and in the vector channel. The main impact of the 8-quark scalar channel is to reduce the onset of quark matter, while the 8-quark vector channel acts to stiffen the equation of state at high densities. Within the parameter space where the 4-quark vector channel is small, and the 8-quark vector channel sizeable, stable stars with masses of 2 M ⊙ and above are found to hold quark matter in their cores.
Highlights
One of the most severe constraints of the equation of state (EoS) of QCD at extreme densities comes from the recent 2M mass determinations of PSR J1614-2230 [1] and PSR J0348-0432 [2] having important consequences for the existence of quark matter in compact stars [3,4,5,6].In this work we assume compact stars are the so-called hybrid stars, composed of a nuclear mantle and a quark core
In order to obtain heavy hybrids stars, quark matter EoS should be stiff, with a low onset [7]. This can be achieved in the MIT bag model by perturbative corrections to the EoS and small bag pressures [8], while within the Nambu–Jona-Lasinio (NJL) model large vector channel is used for stiffness [9], while shift in the vacuum energy [10,11] or introduction of superconductivity ensures low onset [12]
We point out that an alternative microscopic picture is possible with multiquark interactions: whereas stiffening of the EoS is provided by the 8-quark vector channel interaction, lowering of the onset is accomplished by introducing a sizeable 8-quark scalar channel interaction and keeping the 4-quark vector channel interaction small
Summary
One of the most severe constraints of the equation of state (EoS) of QCD at extreme densities comes from the recent 2M mass determinations of PSR J1614-2230 [1] and PSR J0348-0432 [2] having important consequences for the existence of quark matter in compact stars [3,4,5,6]. In order to obtain heavy hybrids stars, quark matter EoS should be stiff, with a low onset [7]. We propose an alternative scenario by taking into account the fact that NJL is a non-renormalizable effective model, valid up to some scale Λ. As we approach this scale, say by increasing the chemical potential, higherdimensional operators should become important. It has been pointed out [16,17] that including higher scalar interactions can reduce the critical temperature in the NJL model, bringing it in closer agreement with lattice results at finite temperature [18]. We demonstrate that the mass of the star can be increased up to and above 2M with the 8-quark vector interaction, while still keeping the 4-quark vector interaction low
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