arXiv subjects

Giuseppe Gaetano Luciano

Publications and source records attributed to Giuseppe Gaetano Luciano.

At least 37 records · Page 2Linked to original sources

arXiv2025

Constraints on Barrow and Tsallis Holographic Dark Energy from DESI DR2 BAO data

Barrow and Tsallis Holographic Dark Energy (HDE) are two recently proposed extensions of the standard HDE framework, incorporating generalized corrections to horizon entropy through the use of Barrow and Tsallis entropies. Tsallis entropy arises from non-extensive statistical phenomena which account for long-range correlations and deviations from additivity, while Barrow entropy emerges from quantum-gravitational effects on the horizon geometry, associated with fractal modifications and deformations. At the cosmological level, both scenarios lead to the same equations, nevertheless the involved parameters obey different theoretical bounds. In this work, we use observational data from Supernova Type Ia (SNIa), Cosmic Chronometers (CC) and Baryonic acoustic oscillations (BAO), including the recently released DESI DR2 dataset, to place constraints on both scenaria. We show that both can be in agreement with observations, although they cannot alleviate the $H_0$ tension. However, applying information criteria we deduce that both of them are not favoured comparing to $Λ$CDM concordance cosmological paradigm.

gr-qc↗

arXiv2025

Dark Universe inspired by the Kaluza-Klein gravity and impact on Primordial Gravitational Waves

We explore the potential implications of Kaluza-Klein (KK) gravity in unifying the dark sector of the Universe. Through dimensional reduction in KK gravity, the 5D spacetime framework can be reformulated in terms of a 4D spacetime metric, along with additional scalar and vector fields. From the 4D perspective, this suggests the existence of a tower of particle states, including KK gravitons with spin-0 and spin-1 states, in addition to the massless spin-2 gravitons of general relativity (GR). The key idea in the present paper is the analogy with superconductivity theory. By assuming a minimal coupling between an additional complex scalar field and the gauge field, a "mass" term emerges for the spin-1 gravitons. This, in turn, leads to long-range gravitational effects that could modify Newton's law of gravity through Yukawa-type corrections. Assuming an environment-dependent mass for the spin-1 graviton, near the galactic center the repulsive force from this spin-1 graviton is suppressed by an additional attractive component from Newton's constant corrections, resulting in a Newtonian-like, attraction-dominated effect. In the galaxy's outer regions, the repulsive force fades due to its short range, making dark matter appear only as an effective outcome of the dominant attractive corrections. This approach also explains dark matter's emergence as an apparent effects on cosmological scales while our model is equivalent to the scalar-vector-tensor gravity theory. Finally, we examine the impact of dark matter on the primordial gravitational wave (PGW) spectrum and show that it is sensitive to dark matter effects, providing an opportunity to test this theory through future GW observatories.

gr-qc↗

arXiv2025

Quantum Entropy-Driven Modifications to Holographic Dark Energy in $f(G,T)$ Gravity

We present a $f(G,T)$ gravity-based reconstruction of Barrow Holographic Dark Energy (BHDE). This approach extends the conventional HDE model by replacing the Bekenstein-Hawking entropy with Barrow entropy, which encapsulates quantum gravitational corrections to the geometry of black hole horizons. We explore the cosmological dynamics of a flat FRW background filled with a pressureless dust fluid, considering both conserved and non-conserved energy-momentum tensor models. To this end, we employ the Hubble horizon as the infrared cutoff and adopt a power-law ansatz for the scale factor. We then investigate the evolution of key cosmological parameters, including the equation-of-state parameter $ ω_{GT} $, the deceleration parameter $ q $, and the squared sound speed $v_s^2$. Furthermore, we explore the dynamical behavior in the $ω_{GT}-ω'_{GT}$ space. In the case of conserved energy-momentum tensor, our findings indicate that the BHDE model evolves from a quintessence-like regime into the phantom domain. This transition supports the current accelerated expansion of the Universe and offers an improvement over the original HDE model, which does not adequately account for the observed phenomenology. The corresponding $ω_{GT}-ω'_{GT}$ trajectory lies within the freezing region. On the other hand, within the non-conserved framework, the BHDE model exhibits phantom-like behavior in the early Universe, subsequently evolving toward either a cosmological constant-like state or a quintessence-like regime. Notably, unlike the conserved scenario, the squared sound speed $v_s^2$ asymptotically attains positive values in the far future. Moreover, the trajectory in the $ω_{GT}-ω'_{GT}$ phase space displays a thawing behavior. Finally, we evaluate the observational viability of our results and compare them with predictions from alternative reconstructed DE models.

gr-qc↗

arXiv2025

Generalized Uncertainty Principle mimicking dynamical Dark Energy: matter perturbations and gravitational wave data analysis

The Generalized Uncertainty Principle (GUP) stands out as a nearly ubiquitous feature in quantum gravity modeling, predicting the emergence of a minimum length at the Planck scale. Recently, it has been shown to modify the area-law scaling of the Bekenstein-Hawking entropy, giving rise to deformed Friedmann equations within Jacobson's approach. The ensuing model incorporates the GUP correction as a quintessence-like dark energy that supplements the cosmological constant, influencing the dynamics of the early Universe while aligning with the $Λ$CDM paradigm in the current epoch. In this extended scenario, we examine the growth of matter perturbations and structure formation employing the Top-Hat Spherical Collapse approach. Our analysis reveals that the profile of the density contrast is sensitive to the GUP parameter $β$, resulting in a slower gravitational evolution of primordial fluctuations in the matter density. We also discuss implications for the relic density of Primordial Gravitational Waves (PGWs), identifying the parameter space that enhances the PGW spectrum. Using the sensitivity of the next-generation GW observatories in the frequency range below $10^3\,\mathrm{Hz}$, we constrain $β\lesssim10^{39}$, which is more stringent than most other cosmological/astrophysical limits. This finding highlights the potential role of GWs in the pursuit of understanding quantum gravity phenomenology.

gr-qc↗

arXiv2024

Lagrangian formulation of the Tsallis entropy

We investigate the gravitational origin of the Tsallis entropy, characterized by the nonadditive index $δ$. Utilizing Wald's formalism within the framework of $f(R)$ modified theories of gravity, we evaluate the entropy on the black hole horizon for constant curvature solutions to the spherically symmetric vacuum field equations. In so doing, we demonstrate that the Tsallis entropy can be effectively derived from a generalization of the Lagrangian $\mathcal{L}\propto R^{1+ε}$, where $ε=δ-1$ quantifies small deviations from general relativity. In conclusion, we examine the physical implications of our findings in light of cosmological observations and elaborate on the possibility of solving the thermodynamic instability of Schwarzschild black holes.

gr-qc↗

arXiv2024

Four $\mathbb{S}\mathbb{T}\mathbb{U}$ Black Holes Shadows

In this work, we examine the optical behaviors and thermodynamic phase structures using shadow analysis for four $\mathbb{S}\mathbb{T}\mathbb{U}$ black holes. The study is conducted for four cases of charge configurations on the parameter space $\mathcal{M}\left(q_1,q_2,q_3,q_4\right)$. As a matter of fact, both the electric charge as a parameter and the parameter space $\mathcal{M}\left(q_1,q_2,q_3,q_4\right)$ affect the geometry of the black hole shadow, particularly the size of the shadow. We also introduce a constraint on the charge of the black hole from the observational results of the M87$^\star$ {\color{black}and Sgr A$^\star$} shadow. Furthermore, we show that the electric charge and the parameter space $\mathcal{M}\left(q_1,q_2,q_3,q_4\right)$ have a non-trivial impact on the variation of the energy emission rate. Interestingly enough, we find novel scenarios in which the evaporation is slower, which causes the lifetime of the black holes to be considerably elongated. On the other side, the phase structure of four $\mathbb{S}\mathbb{T}\mathbb{U}$ black holes is explored for two cases of electric charge configuration. The findings show a perfect correlation between the shadow and event horizon radii. This correlation is, in fact, helpful in discovering the phase transition in terms of the shadow radius. In addition, the microstructure is being analyzed in terms of shadow analysis, providing similar behavior to the ordinary situation of the Ruppeiner formalism.

gr-qc↗

arXiv2024

Kaniadakis entropy in extreme gravitational and cosmological environments: a review on the state-of-the-art and future prospects

Kaniadakis ($κ$-deformed) statistics is being widely used for describing relativistic systems with non-extensive behavior and/or interactions. It is built upon a one-parameter generalization of the classical Boltzmann-Gibbs-Shannon entropy, possessing the latter as a particular sub-case. Recently, Kaniadakis model has been adapted to accommodate the complexities of systems under the influence of gravity. The ensuing framework exhibits a rich phenomenology that allows for a deeper understanding of the most extreme conditions of the Universe. Here we present the state-of-the-art of $κ$-statistics, discussing its virtues and drawbacks at different energy scales. Special focus is dedicated to gravitational and cosmological implications, including effects on the expanding Universe in dark energy scenarios. This review highlights the versatility of Kaniadakis paradigm, demonstrating its broad application across various fields and setting the stage for further advancements in statistical modeling and theoretical physics.

astro-ph.CO↗

arXiv2024

Cosmology from String T-duality and zero-point length

Inspired by String T-duality and taking into account the zero-point length correction, $l_0$, to the gravitational potential, we construct modified Friedmann equations by applying the first law of thermodynamics on the apparent horizon of the Friedmann-Robertson-Walker (FRW) Universe. The cosmological viability of this extended scenario is investigated by studying influences on the evolution of the early Universe and performing the cosmographic analysis. Furthermore, we explore the inflationary paradigm under the slow-roll condition. By testing the model against observational data, the zero-point length is constrained around the Planck scale, in compliance with the original assumption from String T-duality. We also study the growth of density perturbations in the linear regime. It is shown that the zero-point length stands out as an alternative characterization for the broken-power-law spectrum, which provides a better fitting for the experimental measurements comparing to the simple power-law potential. Finally, we focus on implications for the primordial gravitational waves (PGWs) spectrum. Should the zero-point length be running over energy scales, as is the case for all parameters and coupling constants in quantum gravity under renormalization group considerations, deviations from General Relativity (GR) might be potentially tested through upcoming PGW observatories.

gr-qc↗

arXiv2024

Imprints of Barrow-Tsallis Cosmology in Primordial Gravitational Waves

Both the Barrow and Tsallis $δ$ entropies are one-parameter generalizations of the black-hole entropy, with the same microcanonical functional form. The ensuing deformation is quantified by a dimensionless parameter $Δ$, which in the case of Barrow entropy represents the anomalous dimension, while in Tsallis' case, it describes the deviation of the holographic scaling from extensivity. Here, we utilize the gravity-thermodynamics conjecture with the Barrow--Tsallis entropy to investigate the implications of the related modified Friedmann equations on the spectrum of primordial gravitational waves. We show that, with the experimental sensitivity of the next generation of gravitational wave detectors, such as the Big Bang Observer, it will be possible to discriminate deviations from the $Λ$CDM model up to $Δ\lesssim\mathcal{O}(10^{-3})$.

gr-qc↗

arXiv2023

Time-energy uncertainty relation for neutrino oscillations: historical development, applications and future prospects

Time-energy uncertainty relation (TEUR) plays a fundamental role in quantum mechanics, as it allows to grasp peculiar aspects of a variety of phenomena based on very general principles and symmetries of the theory. Using the Mandelstam-Tamm method, TEUR has been recently derived for neutrino oscillations by connecting the uncertainty on neutrino energy with the characteristic time-scale of oscillations. Interestingly enough, the suggestive interpretation of neutrinos as unstable-like particles has proved to naturally emerge in this context. Further aspects have been later discussed in semiclassical gravity by computing corrections to the neutrino energy uncertainty in a generic stationary curved spacetime, and in quantum field theory, where the clock observable turns out to be identified with the non-conserved flavor charge operator. In the present work, we give an overview on the above achievements. In particular, we analyze the implications of TEUR and explore the impact of gravitational and non-relativistic effects on the standard condition for neutrino oscillations.

hep-th↗

arXiv2023

Slow-roll inflation and growth of perturbations in Kaniadakis modification of Friedmann cosmology

Kaniadakis entropy is a one-parameter deformation of the classical Boltzmann-Gibbs-Shannon entropy, arising from a self-consistent relativistic statistical theory. Assuming a Kaniadakis-type generalization of the entropy associated with the apparent horizon of Friedmann-Robertson-Walker (FRW) Universe and using the gravity-thermodynamics conjecture, a new cosmological scenario is obtained based on the modified Friedmann equations. By employing such modified equations, we analyze the slow-roll inflation, driven by a scalar field with power-law potential, at the early stages of the Universe. We explore the phenomenological consistency of this model by computation of the scalar spectral index and tensor-to-scalar ratio. Comparison with the latest Planck data allows us to constrain Kaniadakis parameter to $κ\lesssim\mathcal{O}(10^{-12}\div10^{-11})$, which is discussed in relation to other observational bounds in the past literature. We also disclose the effects of Kaniadakis correction term on the growth of perturbations at the early stages of the Universe by employing the spherically symmetric collapse formalism in the linear regime of density perturbations. We find out that the profile of density contrast is non-trivially affected in this scenario. Interestingly enough, we observe that increasing Kaniadakis parameter $κ$ corresponds to a faster growth of perturbations in a Universe governed by the corrected Friedmann equations. Finally, we comment on the consistency of the primordial power spectrum for scalar perturbations with the best data-fit provided by Planck.

gr-qc↗

arXiv2023

Neutrino decoherence and violation of the strong equivalence principle

We analyze the dynamics of neutrino Gaussian wave-packets, the damping of flavor oscillations and decoherence effects within the framework of extended theories of gravity. In particular, we show that, when the underlying description of the gravitational interaction admits a violation of the strong equivalence principle, the parameter quantifying such a violation modulates the wave-packet spreading, giving rise to potentially measurable effects in future neutrino experiments.

gr-qc↗

arXiv2023

Kaniadakis entropy-based characterization of IceCube PeV neutrino signals

Kaniadakis $κ$-thermostatistics is by now recognized as an effective paradigm to describe relativistic complex systems obeying power-law tailed distributions, as opposed to the classical (exponential-type) decay. It is founded on a non-extensive one-parameter generalization of the Bekenstein-Hawking entropy, which, in the cosmological framework, gives rise to modified Friedmann equations on the basis of the gravity-thermodynamic conjecture. Assuming the entropy associated with the apparent horizon of the Friedmann-Robertson-Walker (FRW) Universe follows Kaniadakis prescription, in this work we analyze the observed discrepancy between the present bound on the Dark Matter relic abundance and the IceCube high-energy ($\sim 1\,\mathrm{PeV}$) neutrinos. We show that this tension can be alleviated in the minimal model of Dark Matter decay with Kaniadakis-governed Universe evolution, while still considering the 4-dimensional Yukawa coupling between Standard Model and Dark Matter particles. This argument phenomenologically supports the need for a Kaniadakis-like generalization of the Boltzmann-Gibbs-Shannon entropy in the relativistic realm, opening new potential scenarios in high-energy astroparticle physics.

physics.gen-ph↗

arXiv2023

$P-v$ criticalities, phase transitions and geometrothermodynamics of charged AdS black holes from Kaniadakis statistics

Boltzmann entropy-based thermodynamics of charged anti-de Sitter (AdS) black holes has been shown to exhibit physically interesting features, such as $P-V$ criticalities and van der Waals-like phase transitions. In this work we extend the study of these critical phenomena to Kaniadakis theory, which is a non-extensive generalization of the classical statistical mechanics incorporating relativity. By applying the typical framework of condensed-matter physics, we analyze the impact of Kaniadakis entropy onto the equation of state, the Gibbs free energy and the critical exponents of AdS black holes in the extended phase space. Additionally, we investigate the underlying micro-structure of black holes in Ruppeiner geometry, which reveals appreciable deviations of the nature of the particle interactions from the standard behavior. Our analysis opens up new perspectives on the understanding of black hole thermodynamics in a relativistic statistical framework, highlighting the role of non-extensive corrections in the AdS black holes/van der Waals fluids dual picture.

gr-qc↗

arXiv2023

Coherent states for generalized uncertainty relations as Tsallis probability amplitudes: new route to non-extensive thermostatistics

We study coherent states associated to a generalized uncertainty principle (GUP). We separately analyze the cases of positive and negative deformation parameter $β$, showing that the ensuing probability distribution is a Tsallis distribution whose non-extensivity parameter $q$ is monotonically related to $β$. Moreover, for $β<0$ (corresponding to $q<1$), we reformulate the GUP in terms of a one-parameter class of Tsallis entropy-power based uncertainty relations, which are again saturated by the GUP coherent states. We argue that this combination of coherent states with Tsallis entropy offers a natural conceptual framework allowing to study quasi-classical regime of GUP in terms of non-extensive thermodynamics. We substantiate our claim by discussing generalization of Verlinde's entropic force and ensuing implications in the late-inflation epoch. Corresponding dependence of the $β$ parameter on cosmological time is derived for the reheating epoch. The obtained $β$ is consistent with values predicted by both string-theory models and the naturalness principle. Further salient issues, including derivation of new $β$-dependent expressions for the lowest possible value of the spin and Immirzi parameter in Loop Quantum Gravity, and connection of our proposal with the Magueijo--Smolin doubly special relativity are also discussed. This article provides a more extended and comprehensive treatment of our recent letter [Phys. Rev. D 105, L121501 (2022)].

gr-qc↗

arXiv2023

30 years in: Quo vadis generalized uncertainty principle?

According to a number of arguments in quantum gravity, both model-dependent and model-independent, Heisenberg's uncertainty principle is modified when approaching the Planck scale. This deformation is attributed to the existence of a minimal length. The ensuing models have found entry into the literature under the term Generalized Uncertainty Principle (GUP). In this work, we discuss several conceptual shortcomings of the underlying framework and critically review recent developments in the field. In particular, we touch upon the issues of relativistic and field theoretical generalizations, the classical limit and the application to composite systems. Furthermore, we comment on subtleties involving the use of heuristic arguments instead of explicit calculations. Finally, we present an extensive list of constraints on the model parameter $β$, classifying them on the basis of the degree of rigour in their derivation and reconsidering the ones subject to problems associated with composites.

gr-qc↗

arXiv2023

Lagrangian reconstruction of Barrow holographic dark energy in interacting tachyon model

We consider a correspondence between the tachyon dark energy model and Barrow holographic dark energy (BHDE). The latter is a modified scenario based on the application of the holographic principle with Barrow entropy instead of the usual Bekenstein-Hawking one. We reconstruct the dynamics of the tachyon scalar field $T$ in a curved Friedmann-Robertson-Walker Universe both in the presence and absence of interactions between dark energy and matter. As a result, we show that the tachyon field exhibits a non-trivial dynamics. In a flat Universe, $\dot T^2$ must always be vanishing, independently of the existence of interaction. This implies $ω_D=-1$ for the equation-of-state parameter, which in turn can be used for modeling the cosmological constant behavior. On the other hand, for a non-flat Universe and various values of Barrow parameter, we find that $\dot T^2$ decreases monotonically for increasing $\cos(R_h/a)$ and $\cosh(R_h/a)$, where $R_h$ and $a$ are the future event horizon and the scale factor, respectively. Specifically, $\dot T^2\ge0$ for a closed Universe, while $\dot T^2<0$ for an open one, which is physically not allowed. We finally comment on the inflation mechanism and Trans-Planckian Censorship Conjecture in BHDE and discuss observational consistency of our model.

hep-th↗

arXiv2023

Black hole geometrothermodynamics and critical phenomena: a look from Tsallis entropy-based perspective

We analyze geometrothermodynamics of charged anti-de Sitter (AdS) black holes with a global monopole in the framework of Tsallis statistics. The latter arises from a non-additive generalization of Boltzmann-Gibbs entropy, which is still recovered as a particular sub-case. We examine the effects of Tsallis entropy on small-large black holes phase-transitions and critical exponents, comparing the results with the liquid-gas change of phase occurring in van der Waals fluids. We also discuss some physical constraints on Tsallis parameter and the impact on sparsity of BH radiation. Thermodynamic curvature behavior is then explored from a geometric perspective within Ruppeiner formalism on the $S-P$ coordinate space. Similar considerations are extended to charged $(2+1)$-dimensional Banados-Teitelboim-Zanelli (BTZ) black holes by computing the entropy-pressure and entropy volume corrected curvatures. Our analysis shows that Tsallis prescription has non-trivial implications on black hole geometrothermodynamics, emphasizing the role of non-additive entropy on the correspondence between black holes and van der Waals systems.

hep-th↗