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arXiv · 2606.29576

Quark and hybrid stars with renormalization group improvement of NNLO perturbative QCD

Loïc Fernandez·Jean-Loïc Kneur·Marcus Benghi Pinto·Constança Providência·Claudia Ratti·Tulio E. Restrepo
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Abstract

Recently, the NNLO perturbative QCD pressure of cold and dense symmetric matter, with arbitrary quark masses, has been resummed within the renormalization-group-optimized perturbation theory (RGOPT) framework. By being imbued with renormalization group properties, the resulting pressure is less sensitive to renormalization scale ($\Lambda\equiv X \mu_B/3$) variations than the NNLO perturbative QCD pressure. Here, we extend this by considering $\beta$-equilibrium and charge neutrality to evaluate the corresponding equation of state (EoS). We provide a compact ``pocket" fitting formula for the EoS for $N_f=2+1$ massive quarks at different renormalization scale parameter ($X$) values. We describe pure quark stars as well as hybrid stars with quark-cores. Pure quark stars compatible with astrophysical observations were obtained with $X=3.08-3.58$, whereas a larger value (4.10) is needed if the low mass object of the observation GW190814 represents a neutron star. Hybrid stars were built considering three representative hadron models based on a relativistic mean-field description, and chosen to produce soft and stiff EoSs. Stable hybrid stars with masses compatible with the massive pulsar PSR J0740+6620 were obtained considering $X$ of the order of 2 to 2.60-2.98, the largest scale giving rise to hybrid stars with a large quark core with a radius of 5 to 8 km, and the smallest to a small quark core at the center of the star.

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Loïc Fernandez, Jean-Loïc Kneur, Marcus Benghi Pinto, Constança Providência, Claudia Ratti, Tulio E. Restrepo. 2026-06-28. Quark and hybrid stars with renormalization group improvement of NNLO perturbative QCD. https://arxiv.org/abs/2606.29576

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