Abstract
Nonperturbative equations of state (EoSs) for two and three quark flavors are constructed with the functional renormalization group (FRG) within a quark-meson model truncation augmented by vector mesons for low temperature and high density. Based on previous FRG studies without repulsive vector meson interactions the influence of isoscalar vector ω- and ϕ-mesons on the dynamical fluctuations of quarks and (pseudo)scalar mesons is investigated. The grand potential as well as vector meson condensates are evaluated as a function of quark chemical potential and the quark matter EoS in β-equilibrium is applied to neutron star (NS) physics. The tidal deformability and mass-radius relations for hybrid stars from combined hadronic and quark matter EoSs are compared for different vector couplings. We observe a significant impact of the vector mesons on the quark matter EoS such that the resulting EoS is sufficiently stiff to support two-solar-mass neutron stars.
Highlights
The European Physical Journal Special Topics by the LIGO/Virgo/Kagra collaboration or via various projects such as the Einstein Telescope or the Cosmic Explorer are promising tools to reduce uncertainties.despite this bright future on the experimental side, a precise determination of the underlying equations of state (EoSs) will not be fully conclusive because on the theoretical side the equation of state (EoS) alone cannot resolve for the detailed matter composition and interactions
For Nf = 2 + 1, the transition generally occurs at lower pressures and with larger ∆ε than for Nf = 2 due to the additional strange degree of freedom in the quark matter EoS
Based on a previous work [56] a two- and three flavor quark-meson model that fully incorporates chiral symmetry breaking has been augmented with vector mesons to investigate the quark matter EoS relevant for neutron star physics
Summary
The European Physical Journal Special Topics by the LIGO/Virgo/Kagra collaboration or via various projects such as the Einstein Telescope or the Cosmic Explorer are promising tools to reduce uncertainties. Towards lower densities the quarks cluster into nucleons and the emergence of long-range correlations between nucleons will increasingly complicate the QCD-based FRG approach [53,54,55] Within this framework, the impact of fluctuations in the (pseudo)scalar interaction channel on the compact star EoS has recently been studied [56]. The inclusion of a repulsive vector interaction in the quark-meson model should stiffen the quark matter EoS, leading to a higher speed of sound and allowing for constructing hybrid stars compatible with observations Within this first study, we neglect the possibility of diquark pairing and do not enter the discussion of the extremely rich phase structure of color superconducting matter in the density range of neutron stars [67,68]. A list of the used input parameters and some technical details for the numerical solution are collected in the appendices
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