We here present a new version of the publicly available general relativistic magnetohydrodynamic (GRMHD) code Spritz, which now includes an approximate neutrino leakage scheme able to handle neutrino cooling and heating. The leakage scheme is based on the publicly available ZelmaniLeak code, with a few modifications in order to properly work with Spritz. We discuss the involved equations, physical assumptions, and implemented numerical methods, along with a large battery of general relativistic tests performed with and without magnetic fields. Our tests demonstrate the correct implementation of the neutrino leakage scheme, paving the way for further improvements of our neutrino treatment and the first application to magnetized binary neutron star mergers. We also discuss the implementation in the Spritz code of high-order methods for a more accurate evolution of hydrodynamical quantities.

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We propose a model of asymmetric bosonic dark matter (DM) with self-repulsion. By adopting the two-fluid formalism, we study different DM distribution regimes, either, fully condensed inside the core of a star, or, otherwise, distributed in a dilute halo around a neutron star (NS). We show that for a given total gravitational mass, DM condensed in a core leads to a smaller radius and tidal deformability compared to a pure baryonic star. This effect may be interpreted as an effective softening of the equation of state. On the other hand, the presence of a DM halo increases the tidal deformability and total gravitational mass. As a result, an accumulated DM inside compact stars could mimic an apparent softening/stiffening of strongly interacting matter EoS and constraints we impose on it at high densities. We limit the model parameter space by confronting the cross section of the DM self-interaction to the constraint extracted from the analysis of the Bullet Cluster. Furthermore, from the analysis of the effect of DM particles, interaction strength, and relative DM fractions inside NSs we obtained a rigorous constraint on model parameters. To identify its impact on NSs we consider the DM fraction may reach up to 5%, which could be considered too high in several scenarios. Finally, we discuss several pieces of smoking gun evidence of the presence of DM that is free from the abovementioned degeneracy between the effect of DM and properties of strongly interacting matter. These signals could be probed with future and ongoing astrophysical and gravitational wave surveys.

We study the impact of asymmetric bosonic dark matter on neutron star properties, including possible changes of tidal deformability, maximum mass, radius, and matter distribution inside the star. The conditions at which dark matter particles tend to condensate in the star’s core or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. To confirm the presence of dark matter in the compact star’s interior, and to break the degeneracy between the effect of accumulated dark matter and strongly interacting matter properties at high densities, several astrophysical and GW tests are proposed.