arXiv subjects

Lorenzo Cipriani

Publications and source records attributed to Lorenzo Cipriani.

6 recordsLinked to original sources

arXiv2026

Hybrid Stars with Post-Merger Rotation Profiles

We study the effect of differential rotation on hybrid stars with the first-order deconfinement phase transition from hadronic to color superconducting quark matter. The differential rotation is introduced within a realistic, four-parameter phenomenological rotation law, in which the maximum angular velocity of the rotating configuration is shifted away from the center. We focus on two classes of differentially rotating solutions, namely quasi-toroidal (type C) and quasi-spherical (type A), and study the changes in the star global properties and angular velocity profiles due to the presence of a phase transition. Thus, we demonstrate the existence of quasi-toroidal hybrid star configurations in which deconfined quark matter forms a ring around the center of mass, while hadronic matter remains at the center and outer layers. Furthermore, we show that when increasing the angular momentum $J$ the turning points of the $J=const$ sequences shift towards lower energy densities, shrinking considerably the region where differentially rotating neutron stars with phase transitions exists. Interestingly, for both type A and type C solutions, the angular velocity profile is continuous throughout the star despite the discontinuity in the energy density. Moreover, we show that at the crossing points where the mass-radius curves for different equations of state intersect, the rotational profiles of the solutions are very close despite large differences in the energy density profiles. This reveals a possible degeneracy between the post-merger remnant properties for models with and without phase transitions, emphasizing the need for complementary multi-messenger observables to distinguish between them.

gr-qc↗

arXiv2025

Differentially rotating neutron stars with dark matter cores

Dark matter is expected to accumulate inside neutron stars, modifying the structure of isolated stars and influencing both the dynamics of binary mergers and the evolution of the resulting hypermassive remnants. Since differential rotation is the primary mechanism delaying the collapse of these remnants, understanding its behavior is crucial when assessing the impact of an embedded dark component. In this work, we extend the numerical code RNS to describe two gravitationally coupled fluids in differential rotation, with baryonic matter modeled by a realistic nuclear equation of state and dark matter represented as a self-interacting bosonic condensate. Within this framework, we construct equilibrium sequences for a representative differential rotation law, providing a basis to explore how dark matter may influence the global properties and rotational dynamics of binary neutron star remnants.

astro-ph.HE↗

arXiv2025

Stellar collapse with pressure in effective loop quantum gravity

We explore semiclassical stellar collapse scenarios with pressure within the framework of effective loop quantum gravity. The objective of this work is to generalize existent models of semiclassical dust collapse and examine the role of pressure in the formation of shell-crossing singularities in a semiclassical context. Numerical investigations show that the shell-focusing singularity characterizing the end state of any classical stellar collapse is here resolved by quantum gravitational effects and replaced by a bounce of the star. However, they also show that shell-crossing singularities remain a general feature of these models and that the inclusion of pressure does not alter the qualitative picture emerging from semiclassical models of inhomogeneous dust collapse. Given the absence of a shell-focusing singularity and the possibility of extending spacetime in the future of the trapped region formed by gravitational collapse, the investigation of the causal structure of the spacetime describing the semiclassical collapse of a star is inevitably tied to a better understanding of the physics of these shell-crossing singularities.

gr-qc↗

arXiv2025

Rapidly spinning dark matter-admixed neutron stars

Millisecond pulsars, representing the older neutron star population, are believed to have undergone a prolonged period of dark matter accumulation, resulting in a higher dark matter content. Their extreme rotation makes them unique laboratories for studying rapidly rotating neutron stars admixed with dark matter. In this work, we model uniformly rotating neutron stars with a dark matter component that rotates independently from the baryon matter, allowing for the investigation of both co-rotating and counter-rotating scenarios. We examine the impact of dark matter rotation on the macroscopic properties of neutron stars, including the mass-radius relation, the mass-shedding Keplerian limit, and moments of inertia, for various dark matter particle masses and total fractions, considering both core and halo distributions. Our findings provide a more comprehensive understanding of how dark matter influences the equilibrium properties of rotating neutron stars, offering new insights into the astrophysical implications of self-interacting dark matter.

astro-ph.HE↗

arXiv2024

Gravitational collapse in effective loop quantum gravity: beyond marginally bound configurations

We study gravitational collapse in effective loop quantum gravity, focusing on non-marginally bound configurations in Lemaître-Tolman-Bondi spacetimes. In the homogeneous limit we recover the effective dynamics of loop quantum cosmology for Friedman cosmologies with spatial curvature. We study a particular family of configurations with a homogeneous interior and a sharp boundary where the dust energy density rapidly and continuously decreases to zero. For these configurations, the gravitational collapse continues to the Planck regime when a bounce occurs, at which point the dust ball starts to expand, and a shock wave forms in the gravitational field within the order of a Planck time after the bounce. The shock slowly moves outwards, eventually reaching the horizon which then disappears, at which time there is no longer a black hole. If the initial configuration is bound, the shock asymptotes to a maximal radius, whereas for unbound initial configurations the shock escapes to infinity. In all cases, the black hole lifetime is proportional to the square of the black hole mass, and additionally depends on how strongly bound the dust profile is; this last quantity also affects the vacuum region outside the dust profile which is not solely determined by the black hole mass and charge as in spherically symmetric general relativity. We also use numerics to study a wide range of other types of initial configurations, both bound and unbound, with qualitatively similar results.

gr-qc↗

arXiv2024

Superfluid dark stars

We present a superfluid dark star model consisting of relativistic dark bosons with two-body self-interaction. The obtained masses, radii, and tidal deformability depend in a simple way on the boson mass and interaction strength. We report first results on binary mergers: the distinctive amplitude and frequency of the emitted gravitational waves are well within reach of terrestrial interferometers.

astro-ph.CO↗