arXiv subjects

Salvatore Capozziello

Publications and source records attributed to Salvatore Capozziello.

At least 73 records · Page 4Linked to original sources

arXiv2025

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

astro-ph.CO↗

arXiv2025

Does DESI 2024 Confirm $Λ$CDM?

We demonstrate that a $\sim 2 σ$ discrepancy with the Planck-$Λ$CDM cosmology in DESI Luminous Red Galaxy (LRG) data in the redshift range $0.4 < z < 0.6$ with effective redshift $z_{\textrm{eff}} = 0.51$ translates into an unexpectedly large $Ω_m$ value, $Ω_m = 0.67^{+0.18}_{-0.17}$. We independently confirm that this anomaly drives the preference for $w_0 > -1$ in DESI data \textit{alone} confronted to the $w_0 w_a$CDM model. Given that LRG data at $z_{\textrm{eff}} = 0.51$ is at odds with Type Ia supernovae in overlapping redshifts, we expect that this anomaly will decrease in statistical significance with future DESI data releases leaving an increasing $Ω_m$ trend with effective redshift at higher redshifts. We estimate the current significance of the latter in DESI data at $\sim 1.8 σ$ and comment on how it dovetails with independent observations. It is imperative to understand what makes DESI LRG data at $z_{\textrm{eff}} = 0.51$ an outlier when it comes to $Ω_m$ determinations.

astro-ph.CO↗

arXiv2025

Null geodesics, causal structure, and matter accretion in Lorentzian-Euclidean black holes

Recently, we introduced the Lorentzian-Euclidean black hole, a static and spherically symmetric solution of vacuum Einstein equations that exhibits a change in metric signature across the event horizon. In this framework, the analysis of radial trajectories of freely falling bodies proves that the central singularity can be avoided via a mechanism we interpret as atemporality, which is responsible for the shift of the time variable from real to imaginary values. In this paper, we further explore this model by first examining the behavior of null geodesics. Our investigation requires a set of signature-adaptive coordinate changes that generalize the local Lorentz transformations underlying General Relativity. We find that photon orbits, like their massive counterparts, cannot traverse the event horizon, thereby strengthening the previous result on the impossibility to reach the $r=0$ singularity. Additionally, we discuss the causal structure of the spacetime, provide the corresponding Penrose diagram, and analyze the process of matter accretion in the outer region of the black hole.

gr-qc↗

arXiv2025

Modified Kerr black holes surrounded by dark matter spike

We study supermassive black holes (SMBH), surrounded by a dark matter (DM) spike, that can be found at the centers of Milky Way and $\text{M87}$ galaxies and are accompanied by a specific kind of topological defect. The investigation is developed within the framework of Bumblebee Gravity with a global monopole (BGGM). The dark matter spike is described by a power-law density profile. Our main objective is to assess how the background arising from spontaneous Lorentz symmetry breaking and the presence of a global monopole influence the properties of the Kerr BH within the region affected by the spike. Using a spherically symmetric static BH with BGGM properties as the seed metric, we construct a non-rotating spacetime with a DM spike, resulting in a BGGM-motivated Schwarzschild-like BH by solving the modified Tolman-Oppenheimer-Volkoff equations (TOV). Next, we extend this approach to the case of a rotating spacetime resulting in the BGGM-motivated Kerr-like BH (BGMKLBH). This approach allows us to explore the spacetime structure, and the BGMKLBH shadows. Then, using available observational data for the DM spike density and considering the effects of BGGM on $\text{Sgr A}^{*}$ and $\text{M87}^{*}$ SMBHs, we analyse the shapes of their shadows and put constraints on the BGGM parameter. Thus, we infer that the BGMKLBHs could be reliable candidates for the astrophysical BHs.

gr-qc↗

arXiv2025

Atemporality from Conservation Laws of Physics in Lorentzian-Euclidean Black Hole

Recent results have shown that singularities can be avoided from the general relativistic standpoint in Lorentzian-Euclidean black holes by means of the transition from a Lorentzian to an Euclidean region where time loses its physical meaning and becomes imaginary. This dynamical mechanism, dubbed ``atemporality'', prevents the emergence of black hole singularities and the violation of conservation laws. In this paper, the notion of atemporality together with a detailed discussion of its implications is presented from a philosophical perspective. The main result consists in showing that atemporality is naturally related to conservation laws.

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↗

arXiv2025

The Hamilton equations in $f(T)$ teleparallel gravity and in New General Relativity

We derive the Hamiltonian function for extended teleparallel theories of gravity in their covariant formulation. In particular, we present the Hamiltonian for $f(T)$ gravity and New General Relativity. From this, we obtain the related Hamilton equations, which are presented both in covariant formulation and Weitzenböck gauge. In this framework, teleparallel equivalent to General Relativity, its $f(T)$ extension and New General Relativity can be compared. We find that $f(T)$ and New General Relativity consistently reduce to the Teleparallel Equivalent to General Relativity, while significant differences appear comparing the Hamilton equations of $f(T)$ with $f(R)$ gravity.

gr-qc↗

arXiv2025

Extended Geometric Trinity of Gravity

Extensions of equivalent representations of gravity are discussed in the metric-affine framework. First, we focus on: (i) General Relativity, based upon the metric tensor whose dynamics is given by the Ricci curvature scalar $R$; (ii) the Teleparallel Equivalent of General Relativity, based on tetrads and spin connection whose dynamics is given by the torsion scalar $T$; (iii) the Symmetric Teleparallel Equivalent of General Relativity, formulated with respect to both the metric tensor and the affine connection and characterized by the non-metric scalar $Q$ with the role of gravitational field. They represent the so-called Geometric Trinity of Gravity, because, even if based on different frameworks and different dynamical variables, such as curvature, torsion, and non-metricity, they express the same gravitational dynamics. Starting from this framework, we construct their extensions with the aim to study possible equivalence. We discuss the straightforward extension of General Relativity, the $f(R)$ gravity, where $f(R)$ is an arbitrary function of the Ricci scalar. With this paradigm in mind, we take into account $f(T)$ and $f(Q)$ extensions showing that they are not equivalent to $f(R)$. Dynamical equivalence is achieved if boundary terms are considered, that is $f(T-\tilde{B})$ and $f(Q-B)$ theories. The latter are the extensions of Teleparallel Equivalent of General Relativity and Symmetric Teleparallel of General Relativity, respectively. We obtain that $f(R)$, $f(T-\tilde{B})$, and $f(Q-B)$ form the Extended Geometric Trinity of Gravity. The aim is to show that also if dynamics are equivalent, foundations of theories of gravity can be very different.

gr-qc↗

arXiv2025

The Weinberg no-go theorem for cosmological constant and nonlocal gravity

We show how a nonlocal gravitational interaction can circumvent the Weinberg no-go theorem on cosmological constant, which forbids the existence of any solution to the cosmological constant problem within the context of local field theories unless some fine-tuning is assumed. In particular, Infinite Derivative Gravity theories hint at a possible understanding of the cosmological constant as a nonlocal gravitational effect on very large scales. In this perspective, one can describe the observed cosmic acceleration in terms of an effective field theory without relying on the fine-tuning of parameters or additional matter fields.

gr-qc↗

arXiv2025

Can wormholes mirror the quasi-normal mode spectrum of Schwarzschild black holes?

Wormholes are exotic compact objects characterized by the absence of essential singularities and horizons, acting as slender bridges linking two distinct regions of spacetime. Despite their theoretical significance, they remain however undetected, possibly due to their ability to closely mimic the observational properties of black holes. This study explores whether a static and spherically symmetric wormhole within General Relativity can reproduce the quasi-normal mode spectrum of a Schwarzschild black hole under scalar, electromagnetic, and axial gravitational perturbations, both individually and in combination. To address this, we reformulate the wormhole metric components using a near-throat parametrization. Our analysis concentrates on the fundamental mode and first overtone, estimated via the Wentzel-Kramers-Brillouin method. By employing a customized minimization strategy, we demonstrate that within a specific region of the parameter space, a wormhole can successfully replicate a subset of the black hole quasi-normal mode spectrum.

gr-qc↗

arXiv2025

Discriminating among cosmological models by data-driven methods

We explores the Pantheon+SH0ES dataset to identify patterns that can discriminate between different cosmological models. We focus on determining whether the behaviour of dark energy is consistent with the standard $Λ$CDM model or suggests novel cosmological features. The central goal is to evaluate the robustness of the $Λ$CDM model compared with other dark energy models, and to investigate whether there are deviations that might indicate new cosmological insights. The study takes into account a data-driven approach, using both traditional statistical methods and machine learning techniques. Initially, we evaluate six different dark energy models using traditional statistical methods like Markov Chain Monte Carlo (MCMC), Static and Dynamic Nested Sampling to infer the cosmological parameters. Subsequently, we adopt a machine learning approach, developing a regression model to compute the distance modulus of each supernova, expanding the feature set to 74 statistical features. Traditional statistical analysis confirms that the $Λ$CDM model is robust, yielding expected parameter values. Other models show deviations, with the Generalised and Modified Chaplygin Gas models performing poorly. In the machine learning analysis, feature selection techniques, particularly Boruta, significantly improve model performance. In particular, models initially considered weak (Generalised/Modified Chaplygin Gas) show significant improvement after feature selection. The study demonstrates the effectiveness of a data-driven approach to cosmological model evaluation. The $Λ$CDM model remains robust, while machine learning techniques, in particular feature selection, reveal potential improvements in alternative models which could be relevant for new observational campaigns like the recent DESI survey.

astro-ph.CO↗

arXiv2025

Non-locality in Quadrupolar Gravitational Radiation

General Relativity suffers for two main problems which have not yet been overcome: it predicts spacetime singularities and cannot be formulated as a perturbative renormalizable theory. In particular, many attempts have been made for avoiding singularities, such as considering higher order or infinite derivative theories. The price to pay in both cases is to give up locality and therefore they are known altogether as non-local theories of gravity. In this paper, we investigate how to recognize the presence of non-local effects by exploiting the power emitted by gravitational waves in a binary system in presence of non-local corrections as $R\Box^{-1}R$ to the Hilbert-Einstein action. After solving the field equations in terms of the source stress-energy tensor $T_{μν}$ and obtaining the gravitational wave stress-energy pseudo-tensor, $τ_{μν}$, we find that the General Relativity quadrupole formula is modified in a non-trivial way, making it feasible to find a possible signature of non-locality. Our final results on the gravitational wave stress-energy pseudo-tensor could also be applied to several astrophysical scenarios involving energy or momentum loss, potentially providing multiple tests for non-local deviations from General Relativity. We finally discuss the detectability of the massless transverse scalar mode, discovering that, although this radiation is extremely weak, in a small range around the model divergence, its amplitude could fall within the low-frequency Einstein Telescope sensitivity.

gr-qc↗

arXiv2025

Barrow entropies in black hole thermodynamics

We study the thermodynamic features of static, spherically-symmetric Schwarzschild black holes adopting different types of Barrow entropy. Specifically, in addition to the standard Barrow entropy, we consider a logarithmic-corrected type of this entropy by taking into account some loop quantum gravity effects. Moreover, we investigate the black hole thermodynamics from the viewpoint of Barrow entropy in presence of non-extensivity effects coming from the Tsallis statistics. Finally, we compare the results obtained for different Barrow-based entropies.

gr-qc↗

arXiv2025

Observable Signatures of RN Black Holes with Dark Matter Halos via Strong Gravitational Lensing and Constraints from EHT Observations

We investigate the impact of dark matter halos on the gravitational lensing produced by electrically charged, spherically symmetric black holes in the strong-field regime. The study focuses on two dark matter models: the Universal Rotation Curve Model and the cold dark matter model. We derive the coefficients for the strong deflection limit and numerically analyze the deflection angle variations. Graphical representations of the results show that the strong deflection angle, $α_D$ , increases with the charge parameter $Q$ in the presence of a dark matter halo. We explore the astrophysical consequences for the supermassive black holes $M87^*$ and $SgrA^*$ , comparing the results with standard Reissner-Nordström and Schwarzschild black holes via strong gravitational lensing observations. Our findings suggest that charged black holes with dark matter halos can be differentiated from standard black holes. We constrain the charge parameter $Q$ using observational data from the Event Horizon Telescope Collaboration. For $M87^*$ , we find $0 \leq |Q| \leq 0.366M$ with the Universal Rotation Curve model and $0 \leq |Q| \leq 0.364M$ with the cold dark matter model. For $SgrA^*$ , the constraints are $0 \leq |Q| \leq 0.586M$ and $0 \leq |Q| \leq 0.584M$, respectively. These results suggest that charged black holes with dark matter halos satisfy the Event Horizon Telescope constraints, offering potential for future identification in observational campaigns.

gr-qc↗

arXiv2025

Gravity from Pre-geometry

The gravitational interaction, as described by the Einstein-Cartan theory, is shown to emerge as the by-product of the spontaneous symmetry breaking of a gauge symmetry in a pre-geometric four-dimensional spacetime. Starting from a formulation à la Yang-Mills on an SO(1,4) or SO(3,2) principal bundle and not accounting for a spacetime metric, the Einstein-Hilbert action is recovered after the identification of the effective spacetime metric and spin connection for the residual SO(1,3) gauge symmetry of the spontaneously broken phase - i.e. the stabiliser of the SO(1,4) or SO(3,2) gauge group. Thus, the two fundamental tenets of General Relativity, i.e. diffeomorphism invariance and the equivalence principle, can arise from a more fundamental gauge principle. The two mass parameters that characterise Einstein gravity, namely the Planck mass and the cosmological constant, are likewise shown to be emergent, with the correct sign for the cosmological constant depending on whether the fundamental gauge group is taken to be either the de Sitter or the anti-de Sitter group. The phase transition from the unbroken to the spontaneously broken phase is expected to happen close to the Planck temperature. This is conjectured to be dynamically driven by a scalar field that implements a Higgs mechanism, hence providing mass to new particles, with consequences for cosmology and high-energy physics. The couplings of gravity to matter are discussed after drawing up a dictionary that interconnects pre-geometric and effective geometric quantities. In the unbroken phase where the fundamental gauge symmetry is restored, the theory is potentially power-counting renormalisable without matter, offering a novel path towards a UV completion of Einstein gravity.

hep-th↗

arXiv2024

Generalized uncertainty principle corrections in Rastall-Rainbow Casimir wormholes

We explore wormhole solutions sourced by Casimir energy density involving generalized uncertainty principle corrections within the framework of Rastall-Rainbow gravity. The questions of traversability and stability, as well as the presence of exotic matter, are carefully investigated. In particular, the stability issue is addressed via an approach that has not been previously employed in the context of wormholes. This method, which represents an improved version of the so-called Herrera cracking technique, has the potential to yield novel insights in the field of wormhole geometries.

gr-qc↗

arXiv2024

Missing matter in galaxies as a neutrino mixing effect

We show that, in the framework of quantum field theory in curved spacetime, the semiclassical energy-momentum tensor of the neutrino flavor vacuum fulfills the equation of state of dust and cold dark matter. We consider spherically symmetric spacetimes, and we demonstrate that, within the weak field approximation, the flavor vacuum contributes as a Yukawa correction to the Newtonian potential. This corrected potential may account for the flat rotation curves of spiral galaxies. In this perspective, neutrino mixing could contribute to dark matter

hep-ph↗

arXiv2024

High-redshift Cosmology by Gamma-Ray Bursts: an overview

Several correlations among Gamma-Ray Bursts (GRBs) quantities, both in the prompt and afterglow emissions, have been established during the last decades, thus enabling the standardization of GRBs as cosmological probes. Since GRBs are observed up to redshift $z \sim 9$, they represent a valuable tool to fill in the gap of information on the Universe evolution between the farthest type Ia supernovae and the Cosmic Microwave Background Radiation and to shed new light on the current challenging cosmological tensions. Without claiming for completeness, here we describe the state of the art of GRB correlations, their theoretical interpretations, and their cosmological applications both as standalone probes and in combination with other probes. In this framework, we pinpoint the importance of correcting the correlations for selection biases and redshift evolution to derive intrinsic relations, the assets of combining probes at different scales, and the need for the employment of the appropriate cosmological likelihood to precisely constrain cosmological parameters. Furthermore, we emphasize the benefits of the cosmographic approach to avoid any cosmological assumptions and the valuable applications of machine learning techniques to reconstruct GRB light curves and predict unknown GRB redshifts. Finally, we stress the relevance of all these factors, along with future observations, to definitely boost the power of GRBs in cosmology.

astro-ph.CO↗