Comprehensive analysis of constructing hybrid stars with a renormalization group-consistent Nambu-Jona-Lasino model

¹ Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
² Institut für Theoretische Physik, Goethe Universität, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main, Germany
³ Technische Universität Darmstadt, Fachbereich Physik, Institut für Kernphysik, Theoriezentrum, Schlossgartenstr. 2, D-64289 Darmstadt, Germany

^⋆ Corresponding authors: jan-erik.christian@uni-hamburg.de, rather@astro.uni-frankfurt.de, mohammadhossein.gholami@tu-darmstadt.de

Received: 2 April 2025
Accepted: 22 July 2025

Abstract

We investigate the properties of hadronic and quark matter that would allow for a first-order phase transition within neutron stars. To this end, we use a parameterizable relativistic mean-field description for the hadronic phase and a renormalization group-consistent Nambu-Jona-Lasino model for the quark phase. This also enables us to consider sequential phase transitions involving a two-flavor color-superconducting and a color-flavor-locked phase. We find large ranges for all parameters that permit a phase transition, even when constrained by current astrophysical data. We further attempt to filter out parameter sets with a high chance of detectability by mass-radius measurement, i.e., stars with an identical mass but different radii, so-called twin stars. However, we find that such configurations lie outside the constrained parameter spaces. Instead, most of the mass-radius relations that feature a phase transition appear to be indistinguishable from a purely hadronic description.