arXiv subjects

Salvatore Capozziello

Publications and source records attributed to Salvatore Capozziello.

At least 55 records · Page 3Linked to original sources

arXiv2026

The Axion-Photon Mixing and the Extragalactic Magnetic Background: Plateau Regimes, Resonances, and Non-Gaussian Boosts

We present an analytical treatment of Axion-Like-Particle (ALP)--photon mixing with extragalactic background light (EBL) attenuation for constant, Gaussian-stochastic, and non-Gaussian magnetic field configurations--with direct implications for Very High Energy (VHE) gamma-ray observations such as LHAASO, HAWC, and CTA experiments. For constant fields, we derive exact probabilities and identify a perturbative plateau regime where photon survival scales as quartic order of magnetic field, isolating the four-point magnetic correlation as a sensitive probe of non-Gaussianity. For Gaussian stochastic fields, we obtain--for the first time--analytical formulas for non-exponential-decay components in the strong-attenuation regime. Contrary to the widely used domain-like model, photon survival is suppressed by 4-6 orders of magnitude, while both conversion and survival probabilities exhibit distinct multi-peak structures from mass-equal resonance, stochastic resonance, and EBL attenuation. Extending to non-Gaussian fields, we show that non-Gaussianity can enhance photon survival by several orders of magnitude relative to the Gaussian case, potentially explaining the unexpectedly VHE photon event observed by LHAASO. Our results demonstrate that stochastic magnetic fields cannot be reduced to domain-like coherence without losing essential physics, and that VHE gamma-ray spectra encode observable information about both the power spectrum and non-Gaussian structure of intergalactic magnetic fields--critical as next-generation observatories push toward PeV sensitivities.

astro-ph.HE↗

arXiv2026

Constraining $β$-Exponential Inflation with the latest ACT observations

Recent observations from the Atacama Cosmology Telescope (ACT), especially when combined with DESI baryon acoustic oscillation data, indicate a scalar spectral index $n_s$ higher than the value reported by \textit{Planck} 2018, placing tension on universal inflationary attractor models. Motivated by this discrepancy, we investigate the inflationary predictions of the $β$-exponential potential, $V(ϕ)=V_0\left(1-λβϕ/M_p\right)^{1/β}$ considering both minimally and non-minimally coupled realizations. This potential generalizes standard exponential inflation and naturally arises in braneworld scenarios. We derive analytical expressions for the slow-roll parameters and inflationary observables using a perturbative expansion in the non-minimal coupling $ξ$, and validate these results through numerical calculations. In the minimally coupled case, the model predicts $n_s \simeq 0.976$ and $r \simeq 0.035$ for $N=50$ and moderate values of β, remaining compatible with ACT+DESI constraints at the 1σlevel while yielding a spectral tilt larger than the universal attractor prediction. Introducing a small non-minimal coupling significantly improves agreement with observations by suppressing the tensor-to-scalar ratio while preserving the enhanced scalar tilt. For $N=60, λ\sim 0.3-0.5$, and $β\sim O(1-5)$, the non-minimally coupled model yields $n_s \simeq 0.974-0.976$ and $r \lesssim 0.03$, comfortably consistent with ACT, DESI, and BICEP/Keck bounds. Our results show that the $β$-exponential potential, especially when implemented with a non-minimal coupling, exhibits good agreement with the latest CMB observations. Our inflationary predictions of the non-minimal model of $n_s$ and $r$ confirming the leading-order contributions in $ξ$ are sufficient to capture the essential features of both $r$ and $n_s$ in observationally relevant regimes.

gr-qc↗

arXiv2026

NovaMoon: A Strategic Lunar Reference Station for Positioning, Timing, and Largely Enhanced Science in the Earth-Moon System

The renewed interest in lunar exploration and the development of future lunar communication and navigation services highlight the need for a precise, stable, and interoperable geodetic and timing infrastructure on the Moon. NovaMoon, proposed as a scientific and navigation payload for ESA's Argonaut lander, is designed as a lunar-based local differential, geodetic, and timing station supporting both operational needs in the Moon's south polar region and a broad range of scientific investigations. The payload integrates a lunar laser retroreflector, a Very Long Baseline Interferometry transmitter, a receiver for navigation signals compatible with LunaNet standards, high-stability atomic clocks, and direct-to-Earth radio links -- making it the first lunar station to co-locate multiple ranging, tracking, and timing techniques. NovaMoon will enable sub-metre to decimetre positioning, provide local differential corrections for lunar users, and ensure an accurate and stable realisation of position and time. Preliminary simulation studies show that this multi-technique dataset improves the lunar reference frame, orientation and ephemerides, and estimates of interior parameters like tidal response and core properties. NovaMoon will also provide the first long-duration physical realisation of a lunar time reference. Beyond its primary goals, it supports improved cartography, precise surface geolocation, and higher-resolution topography, contributing to safer landings and operations. It also enables new tests of fundamental physics, including constraints on relativity and possible deviations from classical gravity.

astro-ph.EP↗

arXiv2026

Exotic PeVatrons as sources of ultra-high-energy gamma rays

We explore novel classes of exotic astrophysical sources capable of producing ultra-high-energy gamma rays extending beyond the PeV scale, motivated by quantum gravity scenarios and dark matter phenomenology. These sources include: ultra-spinning black hole vortex-string systems; exotic compact objects such as boson star, axion star and Q-ball. Such Exotica generate powerful magnetic fields through interactions with millicharged dark matter, enabling particle acceleration mechanisms that surpass the energy limits of conventional astrophysical sources like pulsar wind nebulae and supernova remnants. We demonstrate that such exotic PeVatrons could be distributed throughout our Galaxy and may be detectable by current (LHAASO, HAWC) and next-generation (CTA) gamma-ray observatories.

astro-ph.HE↗

arXiv2026

The gravitational energy-momentum pseudo-tensor in $f(Q)$ non-metric gravity

We derive the affine tensor associated with the energy and momentum densities of both gravitational and matter fields, the complex pseudo-tensor, for $f(Q)$ non-metric gravity, the straightforward extension of Symmetric Teleparallel Equivalent of General Relativity (STEGR), characterized by a flat, torsion-free, non-metric connection. The local conservation of energy-momentum complex on-shell is satisfied through a continuity equation. An important analogy is pointed out between gravitational pseudo-tensor of teleparallel $f(T)$ gravity, in the Weitzenböck gauge, and the same object of symmetric teleparallel $f(Q)$ gravity, in the coincident gauge. Furthermore, we perturb the gravitational pseudo-tensor $τ^α_{\phantomαλ}$ in the coincident gauge up to the second order in the metric perturbation, obtaining a useful expression for the power carried by the related gravitational waves. We also present an application of the gravitational pseudotensor, determining the gravitational energy density of a Schwarzschild spacetime in STEGR gravity, adopting the concident gauge. Finally, analyzing the conserved quantities on manifolds, the Stokes theorem can be formulated for generic affine connections

gr-qc↗

arXiv2026

Stable black holes in lower dimensional $f(\mathbb{Q})$ non-metric gravity

We investigate exact charged and uncharged black hole solutions in a (2+1)-dimensional spacetime within the framework of quadratic form of $f(\mathbb{Q})$ symmetric teleparallel gravity, where $\mathbb{Q}$ is the non-metricity scalar. By adopting spherical symmetry and considering both vanishing and non-vanishing electromagnetic fields, we derive new classes of black hole solutions and analyze their geometric and physical properties. The study demonstrates that the inclusion of quadratic corrections in the gravitational Lagrangian significantly modifies the structure of solutions, producing deviations from the standard BTZ geometry. Invariants such as curvature and non-metricity scalars are calculated to classify the singularity structure and spacetime behavior. Thermodynamic quantities, including Hawking temperature, entropy, and heat capacity, are computed, showing consistency with the first law of black hole thermodynamics. Furthermore, we examine the geodesic motion of test particles and derive the effective potential to explore the stability of photon orbits. A notable outcome is the identification of weaker black hole singularities in comparison to General Relativity, attributed to the non-metricity corrections. The possibility of multi-horizon configurations is also explored. This study provides a comprehensive analysis of the gravitational, thermodynamic, and dynamical features of lower-dimensional black holes in $f(\mathbb{Q})$ gravity and highlights their distinct characteristics with respect to General Relativity.

gr-qc↗

arXiv2026

Non-local Metric-Affine Gravity

Non-local gravity can potentially solve several problems of gravitational field both at Ultra-Violet and Infra-Red scales. However, such an approach has been formulated mainly in metric formalism. In this paper, we discuss non-local theories of gravity in the metric-affine framework. In particular, we study the dynamics of metric-affine analogue of some well-studied non-local theories, by treating the metric and the connection as independent fields. The approach gives the opportunity to deal with non-local gravity under a more general standard. Furthermore, we introduce some novel non-local metric-affine theories with no Riemannian analogue and investigate their dynamics. Finally we discuss some cosmological applications of our development.

gr-qc↗

arXiv2025

Is Dark Energy Dynamical in the DESI Era? A Critical Review

We investigate whether the recent DESI DR2 measurements provide or not evidences for dynamical dark energy by exploring the $ω_0ω_a$CDM model and its extensions with free $\sum m_ν$ and $N_{\mathrm{eff}}$. Using a comprehensive MCMC analysis with a wide range of cosmological datasets including DESI~DR2 BAO and Ly$α$ data, CMB compressed likelihoods, BBN, cosmic chronometers, and multiple Type~Ia supernova compilations, we assess the statistical preference for departures from $Λ$CDM.

astro-ph.CO↗

arXiv2025

Do low-redshift observations open the doors to an open universe?

The detection of a significant deviation from a zero curvature would have profound consequences for inflationary theories and fundamental physics. Relative to high-redshift Planck's CMB measurements, indicating a $\sim 2σ$ evidence for a closed universe, low-redshift observations of BAO and SN Ia have the advantages of weak dependence on early universe physics, independently observational systematics, and strong redshift dependence of distances in constraining the cosmic curvature. Using the integrated observations from DESI BAO and SN Ia, we find an unexpected $2σ$ evidence for an open universe, regardless of the SN Ia sample employed. When considering DESI, SN Ia and the acoustic scale $θ_\star$ data, the preference for an open universe exceeds the $3σ$ level, reaching $5σ$ for the case of DESY5 Supernovae data. Therefore, low-redshift observations favor an open universe, and this preference persists even when alternative high-redshift priors are adopted. Our results point to the existence of an additional tension between high- and low-redshift observations, present also in non-flat models beyond the minimal $Λ$CDM scheme, thereby challenging the standard inflationary predictions.

astro-ph.CO↗

arXiv2025

Constraints on cosmological parameters and CMB first acoustic peak in conformal Killing gravity

In the frame of conformal Killing gravity cosmology, we performed a Bayesian analysis on two different datasets of Baryon Acoustic oscillations (DESI and SDSS DR16), two datasets of SNeIa (Pantheon+ and Union3), and using the Cosmic Microwave Background (CMB) Planck likelihood. The results for $H_0$ and $Ω_M$ in a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) background are consistent with the $Λ$CDM scenario. We obtain a non-negligible negative value for the novel density of dark sector, $Ω_D$, and its relevance in the evolution of the cosmological observables, thus finding quantitatively what its contribution is on real data to match the standard scenario. The results confirm the dynamical character of dark energy. We also calculate the deceleration parameter $q_0$ and the present time dark energy equation of state parameter $w_0$: the latter belongs to the quintessence regime. The evaluation of the first acoustic peak of CMB places it near to the best value provided by the Planck collaboration. In this scenario, we can conclude that late time and early time data can be successfully matched under the same standard.

gr-qc↗

arXiv2025

Gravitational waves in minimal Maxwell $f(R)$ gravity

We discuss the conversion mechanism from scalar field to gravitational waves in magnetic background in $f(R)$ gravity minimal coupled to the Maxwell electrodynamics. Applying the conversion in early universe with primordial magnetic field and the neutron star with strong magnetosphere, the generated gravitational waves, converted from the scalar field, exhibit distinct power spectra which can be potentially probed by future experiments such as DECIGO, BBO, CE and ET.

gr-qc↗

arXiv2025

Is the $Λ$CDM Model in Crisis?

We present strong evidence for dynamical dark energy that challenges the standard $Λ$CDM model. Several dark energy scenarios are explored, including $ω_0ω_a$CDM, logarithmic, exponential, JBP, and BA parameterizations, along with non-flat cosmologies allowing for spatial curvature ($Ω_k \neq 0$). Our analysis supports a flat Universe with $Ω_k \approx 0$. Using MCMC techniques, we constrain these models with observational data from DESI~DR2 baryon acoustic oscillations, Type~Ia supernovae, and compressed CMB likelihoods. The results provide strong statistical evidence that $ω\neq -1$, favoring dynamical dark-energy behavior consistent with a Quintom-B scenario ($ω_0 > -1$, $ω_a < 0$, and $ω_0 + ω_a < -1$). We also derive upper bounds on the total neutrino mass, $\sum m_ν$, using CMB + DESI~DR2 data: $\sum m_ν< 0.066~\mathrm{eV}$ for $Λ$CDM and $\sum m_ν< 0.075~\mathrm{eV}$ for $ω$CDM. In the non-flat extensions, o$Λ$CDM and o$ω$CDM, the limits relax to $\sum m_ν< 0.263~\mathrm{eV}$ and $\sum m_ν< 0.520~\mathrm{eV}$, respectively. For the other models $ω_0ω_a$CDM, logarithmic, exponential, JBP, BA, and GEDE the constraints range between $<0.043$ and $<0.127~\mathrm{eV}$. The effective number of relativistic species remains consistent with the standard value, $N_{\mathrm{eff}} = 3.044$, across all models. Bayesian evidence further shows that combining DES-SN5Y or Union3 supernova samples with CMB + DESI~DR2 produces measurable deviations from $Λ$CDM. Although no model reaches the $5σ$ significance threshold, several exhibit tensions exceeding $3σ$, suggesting emerging cracks in the cosmological constant paradigm.

gr-qc↗

arXiv2025

Uncertainty Principles and Non-local Black Holes

We discuss the Generalized Uncertainty Principle and the Extended Uncertainty Principle in the context of black hole solutions coming from non-local theories of gravity, focusing, specifically, on Infinite Derivative Gravity. We argue that these modifications of the Heisenberg Uncertainty Principle are effective descriptions arising from the non-local features of gravitational interaction. By comparing the predictions of both the modified uncertainty principles and non-local gravity, we find theoretical constraints on otherwise free parameters as well as universal laws for black hole physics beyond General Relativity.

gr-qc↗

arXiv2025

Does DESI DR2 challenge $Λ$CDM paradigm ?

Although debate on DESI DR1 systematics remains, DESI DR2 is consistent with DR1 and strengthens its trends. In our analysis, the LRG1 point at $z_{\mathrm{eff}}=0.510$ and the LRG3+ELG1 point at $z_{\mathrm{eff}}=0.934$ are in tension with the $Λ$CDM-anchored $Ω_m$ inferred from Planck and SNe Ia (Pantheon$^{+}$, Union3, DES-SN5YR): for LRG1 the tensions are $2.42σ$, $1.91σ$, $2.19σ$, and $2.99σ$; for LRG3+ELG1 they are $2.60σ$, $2.24σ$, $2.51σ$, and $2.96σ$. Across redshift bins DR2 shows improved agreement relative to DR1, with the $Ω_m$ tension dropping from $2.20σ$ to $1.84σ$. Nevertheless, DR2 alone is not decisive against $Λ$CDM, and the apparent deviation is driven mainly by LRG1 and LRG2. In a $ω_0ω_a$CDM fit using all tracers we find a posterior mean with $w_0>-1$, consistent with dynamical dark energy and nominally challenging $Λ$CDM. Removing LRG1 and/or LRG2 restores $Λ$CDM concordance ($ω_0\to-1$); moreover, $ω_0^{\mathrm{(LRG2)}}>w_0^{\mathrm{(LRG1)}}$, indicating that LRG2 drives the trend more strongly. Model selection via the natural-log Bayes factor $\ln\mathrm{BF}\equiv\ln(Z_{Λ\mathrm{CDM}}/Z_{ω_0ω_a\mathrm{CDM}})$ yields weak evidence for $Λ$CDM when LRG1, LRG2, or both are removed, and is inconclusive for the full sample. Hence the data do not require the extra $ω_a$ freedom, and the apparent $ω_0>-1$ preference should be interpreted cautiously as a reflection of the $ω_0$$ω_a$ degeneracy with limited per-tracer information.

astro-ph.CO↗

arXiv2025

Investigating the cosmic distance duality relation with gamma-ray bursts

Deviations from the so-called {\it cosmic distance duality relation} may result from systematic errors in distance measurements or, more interestingly, hint at new physics. Further, it can also be related to the Hubble constant tension between early and local measurements of $H_0$. Based on this, we test validity of this relation through a model-independent parameterization of the Hubble rate via the well-estabilished Bézier polynomials approach. We seek for possible departures from the relation considering three parametrizations, i) a power-law correction, ii) a logarithmic correction and iii) a Padé series $P_{n,m}(z)$ of order (1;2) with $n=1$ being the order of the numerator while $m=2$ is the order of the denominator. Then, assuming a flat scenario, we test them through Monte Carlo -- Markov chain analyses that combine low- and intermediate/high-$z$ data sets, such as observational Hubble data, the Pantheon catalog of type Ia supernovae, galaxy clusters, the second data release from the DESI Collaboration and gamma-ray bursts. In particular, we distinguish between \emph{Analysis A} and \emph{Analysis C}, depending whether the prompt emission $E_{iso}-E_p$ or the prompt-afterglow $L_0-E_p-T$ gamma-ray burst correlations, respectively, is fit together with the other probes previously described. Our results seem to point towards a \emph{no violation} of the cosmic distance duality relation and a preference towards Planck's value of $H_0$.

astro-ph.CO↗

arXiv2025

Equivalent Gravities and Equivalence Principle: Foundations and experimental implications

The so-called Geometric Trinity of Gravity includes General Relativity (GR), based on spacetime curvature; the Teleparallel Equivalent of GR (TEGR), which relies on spacetime torsion; and the Symmetric Teleparallel Equivalent of GR (STEGR), grounded in nonmetricity. Recent studies demonstrate that GR, TEGR, and STEGR are dynamically equivalent, raising questions about the fundamental structure of spacetime, the under-determination of these theories, and whether empirical distinctions among them are possible. The aim of this work is to show that they are equivalent in many features but not exactly in everything. In particular, their relationship with the Equivalence Principle (EP) is different. The EP is a deeply theory-laden assumption, which is assumed as fundamental in constructing GR, with significant implications for our understanding of spacetime. However, it introduces unresolved conceptual issues, including its impact on the nature of the metric and connection, its meaning at the quantum level, tensions with other fundamental interactions and new physics, and its role in dark matter and dark energy problems. In contrast, TEGR and STEGR recover the EP, in particular in its strong formulation, but do not rely on it as a foundational principle. The fact that GR, TEGR, and STEGR are equivalent in non-trivial predictions, but the EP is not necessary for TEGR and STEGR, suggests that it may not be a fundamental feature but an emergent one, potentially marking differences in the empirical content of the three theories. Thus, the developments within the Geometric Trinity framework challenge traditional assumptions about spacetime and may help to better understand some of the unresolved foundational difficulties related to the EP.

gr-qc↗

arXiv2025

Hamiltonian Analysis of Pre-geometric Gravity

The Einstein-Cartan theory of gravity can arise from a mechanism of spontaneous symmetry breaking within the context of pre-geometric gauge theories. In this work, we develop the Hamiltonian analysis of such theories. By making contact with the ADM formalism, we show that all the results of canonical General Relativity are correctly recovered in the IR limit of the spontaneously broken phase. We then apply Dirac's algorithm to study the algebra of constraints and determine the number of degrees of freedom in the UV limit of the unbroken phase. We also discuss possible pathways toward a UV completion of General Relativity, including a pre-geometric generalisation of the Wheeler-DeWitt equation and an extended BF formulation of the pre-geometric theory.

gr-qc↗

arXiv2025

Excess Radiation from Axion-Photon Conversion

Two notable anomalies in radio observations -- the excess radiation in the Rayleigh-Jeans tail of the cosmic microwave background, revealed by ARCADE2, and the twice-deeper absorption trough of the global 21cm line, identified by EDGES -- remain unresolved. These phenomena may have a shared origin, as the enhancement of the 21cm absorption trough could arise from excess heating. We investigate this scenario through the framework of axion-like particles (ALPs), showing that the resonant conversion of ALPs into photons can produce a photon abundance sufficient to resolve both anomalies simultaneously. Our model naturally explains the observed radio excess between 0.4 and 10GHz while also enhances the 21cm absorption feature at 78MHz. Furthermore, it predicts a novel power-law scaling of the radio spectrum above 0.5GHz and an additional absorption trough below 30MHz, which could be verified through cross-detection in upcoming experiments.

astro-ph.CO↗