Stable hybrid stars within a SU(3) quark-meson-model

Abstract

The inner regions of the most massive compact stellar objects might be occupied by a phase of quarks. Since the observations of the massive pulsars PSR J1614-2230 and of PSR J0348+0432 with about two solar masses, the equations of state constructing relativistic stellar models have to be constrained respecting these new limits. We discuss stable hybrid stars, i.e. compact objects with an outer layer composed of nuclear matter and with a core consisting of quark matter (QM). For the outer nuclear layer we utilize a density dependent nuclear equation of state and we use a chiral SU(3) Quark-Meson model with a vacuum energy pressure to describe the objects core. The appearance of a disconnected mass-radius branch emerging from the hybrid star branch implies the existence of a third familiy of compact stars, so called twin stars. Twin stars did not emerge as the transition pressure has to be relatively small with a large jump in energy density, which could not be satisfied within our approach. This is, among other reasons, due to the fact that the speed of sound in QM has to be relatively high, which can be accomplished by an increase of the repuslive coupling. This increase on the other hand yields too high transition pressures for twins stars to appear.

Towards generating a new supernova equation of state: A systematic analysis of cold hybrid stars

“…An increase of c 2 s leads to stronger third-family features in the M-R relation and generally higher maximum masses [7,10,15,58] and thus is favorable for realizing the CCSN explosion mechanism induced by the QCD phase transition. A speed of sound above c 2 s ¼ 1=3 can, e.g., be realized by introducing vector interactions; see [12,15,51,52,59]. Additionally, the influence of extra interaction parameters such as a 2 might be analyzed.…”

“…From this perspective it is acceptable to enforce just one phase transition and ignore the others as is done in the original parameter scans of Fig. 2 and [7,11,11,12,[14][15][16].…”

“…1 In a subsequent work [10], a more detailed analysis was presented and different hadronic EOSs were applied. Zacchi et al [11,12] used the approach of Alford et al for comparison of the results obtained with a newly developed SU(3) quark EOS. A special emphasis was put on the occurrence of twin stars, which are pairs of compact stars at equal masses.…”

Implications of the fermion vacuum term in the extended SU(3) quark meson model on compact star properties

“…These two parameters alone compensate the vacuum contribution in the two condensate equations h n and h s in eqs. (17). It is interesting to note that the grand canonical potential remains unaffected by the choice of the renormalization scale parameter Λ r .…”

Twin stars within the SU(3) chiral quark-meson model

“…The EoS results from the SU(3) Chiral Quark-Meson Model, which is based on the linear σ-model [16,17] and couples mesons and quarks by respecting chiral symmetry. Whereas this model has been previously used within the context of compact stars [18,19], in the present work we go beyond these previous calculations. By scanning the allowed parameter range of the SU(3) Chiral Quark-Meson model -that is the mass of the sigma meson m σ , the vector coupling g ω and the vacuum pressure B 1/4 -we find two stable branches for certain values of the vector coupling and the sigma mass, while keeping the vacuum pressure below B 100 MeV.…”