arXiv subjects

Serena Gambino

Publications and source records attributed to Serena Gambino.

4 recordsLinked to original sources

arXiv2026

Bondi and Novikov-Thorne accretion in regular black holes and Simpson-Visser spacetimes

We compare the Bondi spherical accretion model and the Novikov-Thorne thin disc formalism around regular black holes and Simpson-Visser spacetimes, using several equations of state for the accreting fluids. The Bondi model is significantly more sensitive to spacetime geometry and the equation of state, making it more effective at distinguishing between regular and classical solutions. For the Simpson-Visser solutions, however, increasing the regularisation parameter, $\ell$, shifts critical point positions both inward and outward. However, the charged Simpson-Visser extension, modeled by the charge $Q$, does not produce an effect comparable to that of $\ell$.

gr-qc↗

arXiv2025

Bondi accretion disk luminosity around neutral and charged Simpson-Visser spacetimes

We investigate relativistic Bondi accretion in the Simpson-Visser spacetime, which, via a single parameter $\ell$, interpolates between the Schwarzschild, regular black hole, extremal and wormhole regimes. First, we analyze the neutral Simpson-Visser geometry, recovering Schwarzschild at $\ell=0$, and then its charged extension of the Reissner-Nordström metric. In both these cases, we derive the conservation equations and analyze two representative fluid models: a barotropic perfect fluid and a constituent with an exponential density profile. By varying the parameters across regimes, we locate critical (sonic) points and integrate velocity, density and pressure profiles. While near-horizon inflow velocities are similar across the different solutions, we find that the critical radius and the resulting accretion rates and luminosities severely change, depending on the value of the parameter and type of fluid. Remarkably, the barotropic and exponential cases exhibit different trends in the outer regions. Moreover, by extending the analysis to the charged SV spacetime, we find that the presence of a central charge $Q$ produces additional, albeit modest, shifts in the sonic radius which, in combination with those induced by the regularization parameter $\ell$, could provide a double observational marker. In particular, while $\ell$ acts predominantly on the position of the critical point, in the barotropic fluid case, the electromagnetic contribution of $Q$ slightly dampens the inflow velocity near the horizon.

gr-qc↗

arXiv2025

Comparing Bondi and Novikov-Thorne accretion disk luminosity around regular black holes

We consider and compare the Bondi and Novikov-Thorne accretion mechanisms in spherically symmetric regular black holes. To do so, we model the dark matter distribution adopting two main approaches. The first takes into account a cosmologically-inspired dark fluid, whose pressure turns out to be constant, whereas the density and equation of state depend on the radial coordinate. The second case employs an exponential dark matter energy distribution that describes the dark matter cloud in the accretion process. Accordingly, we quantify the mass accreted by regular solutions with the above information on the energy-momentum tensor and their luminosity and thermal properties, derived from the background models. Numerical simulations of the accretion processes are then reported, comparing regular black holes with Schwarzschild and Schwarzschild-de Sitter metrics. In so doing, we consider the Hayward, Bardeen, Dymnikova and Fang-Wang solutions, where the addiction of a further parameter determines regularity. Implications and physical consequences of using the Novikov-Thorne and Bondi accretion backgrounds are thus critically discussed in varying the free parameters of each spacetime.

gr-qc↗

arXiv2024

Linear perturbations in Horndeski theories with spatial curvature

We analyse the implications of the presence of spatial curvature in modified gravity models. As it is well known, the current standard cosmological model, the $Λ$CDM, is assumed to be spatially flat based on the results of many experiments. However, this statement does not necessarily hold for a modified gravity (MG) model, and this leads to couplings of the spatial curvature with the parameters of the chosen cosmological model. In this paper, we illustrate the theoretical development of how spatial curvature affects the equations of motion at linear order for scalar and tensor perturbations modes using a model-independent approach based on the formalism of the Effective Field Theory (EFT) of dark energy (DE). The results show that spatial curvature gives rise to a coupling with the scalar field perturbations and the functions parameterizing the model.

gr-qc↗