arXiv subjects

Salvatore Capozziello

Publications and source records attributed to Salvatore Capozziello.

At least 145 records · Page 8Linked to original sources

arXiv2022

Testing Born-Infeld $f(T)$ teleparallel gravity through Sgr A$^\star$ observations

We use observational data from the S2 star orbiting around the Galactic Center to constrain a black hole solution of extended teleparallel gravity models. Subsequently, we construct the shadow images of Sgr A$^{\star}$ black hole. In particular, we constrain the parameter $α=1/λ$ which appears in the Born-Infeld $f(T)$ model. In the strong gravity regime we find that the shadow radius increases with the increase of the parameter $α$. Specifically, from the S2 star observations, we find within 1$σ$ that the parameter must lie between $0 \leq α/M^2 \leq 6 \times 10^{-4}$. Consequently, we used the best fit parameters to model the shadow images of Sgr A$^{\star}$ black hole and then using the Gauss-Bonnet theorem we analysed the deflection angle for leading order expansions of the parameter $α$. It is found that within the parameter range, these observables are very close to the Schwarzschild case. Furthermore, using the best fit parameters for the Born-Infeld $f(T)$ model we show the angular diameter is consistent with recent observations for the Sgr A$^{\star}$ black hole angular diameter $(51.8 \pm 2.3) μ$arcsec and difficult to be distinguished from the GR. For the deflection angle of light, in leading order terms, we find that the deflection angle expressed in the ADM mass coincides with the GR, but the ADM mass in the Born-Infeld $f(T)$ gravity increases with the increase of $α$ and the overall deflection angle is expected to me greater in $f(T)$ gravity. As a consequence of this fact, we have shown that the electromagnetic intensity observed in shadow images is smaller compared to GR.

gr-qc↗

arXiv2022

The phase-space view of non-local gravity cosmology

We consider non-local Integral Kernel Theories of Gravity in a homogeneous and isotropic universe background as a possible scenario to drive the cosmic history. In particular, we investigate the cosmological properties of a gravitational action containing the inverse d'Alembert operator of the Ricci scalar proposed to improve Einstein's gravity at both high and low-energy regimes. In particular, the dynamics of a physically motivated non-local exponential coupling is analyzed in detail by recasting the cosmological equations as an autonomous system of first-order differential equations with dimensionless variables. Consequently, we study the phase-space domain and its critical points, investigating their stability and main properties. In particular, saddle points and late-time cosmological attractors are discussed in terms of the free parameters of the model. Finally, we discuss the main physical consequences of our approach in view of dark energy behavior and the $Λ$CDM model.

gr-qc↗

arXiv2022

GINGER

In this paper, we outline the scientific objectives, the experimental layout, and the collaborations envisaged for the GINGER (Gyroscopes IN GEneral Relativity) project. The GINGER project brings together different scientific disciplines aiming at building an array of Ring Laser Gyroscopes (RLGs), exploiting the Sagnac effect, to measure continuously, with sensitivity better than picorad/ s, large bandwidth (ca. 1 kHz), and high dynamic range, the absolute angular rotation rate of the Earth. In the paper, we address the feasibility of the apparatus with respect to the ambitious specifications above, as well as prove how such an apparatus, which will be able to detect strong Earthquakes, very weak geodetic signals, as well as general relativity effects like Lense-Thirring and De Sitter, will help scientific advancements in Theoretical Physics, Geophysics, and Geodesy, among other scientific fields.

gr-qc↗

arXiv2022

Slow-roll inflation in $f(Q)$ non-metric gravity

We discuss the cosmological inflation in the context of $f(Q)$ non-metric gravity, where $Q$ is the non-metric scalar. After introducing conformal transformations for $f(Q)$ gravity, we first focus on the potential-slow-roll inflation by studying the corresponding potentials for different forms of the function $f(Q)$ in the Einstein frame. Secondly, we investigate the Hubble-slow-roll inflation for three classes of inflationary potentials considered for the specific form $f(Q)\propto Q^{2}$, in the Jordan frame. We compare results in both approaches with observations coming from Planck and BICEP2/Keck array satellites. Observational constraints on the parameters space of the models are obtained as well.

gr-qc↗

arXiv2022

Velocity distribution of elliptical galaxies in the framework of Non-local Gravity model

We investigate the velocity distribution of elliptical galaxies in the framework of Non-local Gravity. According to this approach, it is possible to recover the fundamental plane of elliptical galaxies without the dark matter hypothesis. Specifically, we compare theoretical predictions for circular velocity in Non-local Gravity context with the corresponding values coming from a large sample of observed elliptical galaxies. We adopt the surface brightness, effective radius and velocity dispersion as structural parameters for the fundamental plane. As final result, it is possible to show that non-local gravity effects can reproduce the stellar dynamics in elliptical galaxies and fit consistently observational data.

gr-qc↗

arXiv2022

Energy-Momentum Complex in Higher Order Curvature-Based Local Gravity

In General Relativity, there have been many proposals for defining the gravitational energy density, notably those proposed by Einstein, Tolman, Landau and Lifshitz, Papapetrou, Møller, and Weinberg. In this review, we firstly explored the energy--momentum complex in an $n^{th}$ order gravitational Lagrangian $L=L\left(g_{μν}, g_{μν,i_{1}}, g_{μν,i_{1}i_{2}},g_{μν,i_{1}i_{2}i_{3}},\cdots, g_{μν,i_{1}i_{2}i_{3}\cdots i_{n}}\right)$ and then in a gravitational Lagrangian as \mbox{$L_{g}=(\overline{R}+a_{0}R^{2}+\sum_{k=1}^{p} a_{k}R\Box^{k}R)\sqrt{-g}$}. Its gravitational part was obtained by invariance of gravitational action under infinitesimal rigid translations using Noether's theorem. We also showed that this tensor, in general, is not a covariant object but only an affine object, that is, a pseudo-tensor. Therefore, the pseudo-tensor $τ^η_α$ becomes the one introduced by Einstein if we limit ourselves to General Relativity and its extended corrections have been explicitly indicated. The same method was used to derive the energy--momentum complex in $ f\left (R \right) $ gravity both in Palatini and metric approaches. Moreover, in the weak field approximation the pseudo-tensor $τ^η_α$ to lowest order in the metric perturbation $h$ was calculated. As a practical application, the power per unit solid angle $Ω$ emitted by a localized source carried by a gravitational wave in a direction $\hat{x}$ for a fixed wave number $\mathbf{k}$ under a suitable gauge was obtained, through the average value of the pseudo-tensor over a suitable spacetime domain and the local conservation of the pseudo-tensor. As a cosmological application, in a flat Friedmann--Lemaître--Robertson--Walker spacetime, the gravitational and matter energy density in $f(R)$ gravity both in Palatini and metric formalism was proposed.

gr-qc↗

arXiv2022

Revealing Intrinsic Flat $Λ$CDM Biases with Standardizable Candles

Emerging high redshift cosmological probes, in particular quasars (QSOs), show a preference for larger matter densities, $Ω_{m} \approx 1$, within the flat $Λ$CDM framework. Here, using the Risaliti-Lusso relation for standardizable QSOs, we demonstrate that the QSOs recover the \textit{same} Planck-$Λ$CDM Universe as Type Ia supernovae (SN), $Ω_m \approx 0.3$ at lower redshifts $ 0 < z \lesssim 0.7$, before transitioning to an Einstein-de Sitter Universe ($Ω_m =1$) at higher redshifts $z \gtrsim 1$. We illustrate the same trend, namely increasing $Ω_{m}$ and decreasing $H_0$ with redshift, in SN but poor statistics prevent a definitive statement. We explain physically why the trend is expected in the flat $Λ$CDM cosmology, illustrate the intrinsic bias and non-Gaussian tails with mock Pantheon data, and identify a similar trend in BAO below $z=1$. Our results highlight an intrinsic bias in the flat $Λ$CDM Universe, whereby $Ω_m$ increases, $H_0$ decreases and $S_8$ increases with effective redshift, thus providing a new perspective on $Λ$CDM tensions; even in a Planck-$Λ$CDM Universe the current tensions might have been expected.

astro-ph.CO↗

arXiv2022

Dark Energy and Neutrino Superfluids

We show that the neutrino mass, the dark matter and the dark energy can be explained in a unified framework, postulating a new invisible Born-Infeld field, which we name "non-linear dark photon", undergoing a meV-scale dynamical transmutation and coupled to neutrinos. Dark energy genesis is dynamically explained as a byproduct of the dark photon condensation, inducing the bare massless neutrinos to acquire an effective mass around the meV scale. It is fascinating to contemplate the channel induced by the non-linear dark photon leading to the pairing of the non-relativistic neutrinos, hence generating a cosmological superfluid state. As a consequence, the appearance of a light neutrino composite boson is predicted, providing a good cold dark matter candidate. In particular, if our model is enriched by an extra global Lepton number $U_L(1)$ symmetry, then the neutrino pair can be identified with a composite Majoron field with intriguing phenomenological implications for the neutrinoless-double-beta-decay ($0νββ$). Our model carries interesting phenomenological implications since dark energy, dark matter and the neutrino mass are time-varying dynamical variables, as a consequence of the non-linear Born-Infeld interaction terms. Limits arising from PLANCK+SNe+BAO collaborations data are also discussed. Finally, our model allows for an inverse hierarchy of neutrino masses, with interesting implications for the JUNO experiment.

hep-ph↗

arXiv2022

Induced Gravitational Waves from Multi-Sound Speed Resonances during Cosmological Inflation

We explore the possibility of multi-parametric resonances from time varying sound speed during cosmological inflation. In particular, we fix our set-up to the simpler case beyond a single oscillation model already explored in literature: two sinusoidal harmonics around a constant sound speed equal to one. We find that, within the perturbative regime, except for some certain extreme corners of the parameter space, the primordial density spectrum is characterized by two groups of amplified peaks centered around two critical oscillatory frequencies of the sound speed. As a general result, we show that the energy spectrum of the secondary induced GWs from the inflationary era has a single major broad peak, whereas the one from the radiation dominated phase consists of one/two principle peak-like configuration(s) for relatively small/large ratio of two oscillatory frequencies. The GW relic stochastic backgrounds carry a gravitational memory of the parametric resonances during inflation. GW signals from double sound speed resonances can be tested in complementary channels from Pulsar-timing radio-astronomy, space and terrestrial GW interferometers.

astro-ph.CO↗

arXiv2022

Testing non-local gravity by clusters of galaxies

Extended theories of gravity have been extensively investigated during the last thirty years, aiming at fixing infrared and ultraviolet shortcomings of General Relativity and of the associated $Λ$CDM cosmological model. Recently, non-local theories of gravity have drawn increasing attention due to their potential to ameliorate both the ultraviolet and infrared behavior of gravitational interaction. In particular, Integral Kernel theories of Gravity provide a viable mechanism to explain the late time cosmic acceleration so as to avoid the introduction of any form of unknown dark energy. On the other hand, these models represent a natural link towards quantum gravity. Here, we study a scalar-tensor equivalent model of General Relativity corrected with non-local terms, where corrections are selected by the existence of Noether symmetries. After performing the weak field limit and generalizing the results to extended mass distributions, we analyse the non-local model at galaxy cluster scales, by comparing the theoretical predictions with gravitational lensing observations from the CLASH program. We obtain agreement with data at the same level of statistical significance as General Relativity. We also provide constraints for the Navarro--Frenk--White parameters and lower bounds for the non-local length scales. The results are finally compared with those from the literature.

gr-qc↗

arXiv2022

Gamma-Ray Bursts, Supernovae Ia and Baryon Acoustic Oscillations: a binned cosmological analysis

Cosmological probes at any redshift are necessary to reconstruct consistently the cosmic history. Studying properly the tension on the Hubble constant, $H_0$, obtained by Supernovae Type Ia (SNe Ia) and the Planck measurements of the Cosmic Microwave Background Radiation would require complete samples of distance indicators at any epoch. Gamma-Ray Bursts (GRBs) are necessary for the aforementioned task because of their huge luminosity that allows us to extend the cosmic ladder at very high redshifts. However, using GRBs alone as standard candles is challenging because their luminosity varies widely. To this end, we choose a reliable correlation for GRBs with a very small intrinsic scatter: the so-called fundamental plane correlation for GRB afterglows corrected for selection biases and redshift evolution. We choose a well-defined sample: the platinum sample, composed of 50 Long GRBs. To further constrain cosmological parameters, we use Baryon Acoustic Oscillations (BAOs) given their reliability as standard rulers. Thus, we have applied GRBs, SNe Ia, and BAOs in a binned analysis in redshifts so that GRBs' contribution is fully included in the last redshift bin, which reaches $z=5$. We use the fundamental plane correlation together with SNe Ia and BAOs, to constrain $H_0$ and the density matter today, $Ω_{M}$. This methodology allows us to assess the role of GRBs combined with SNe Ia and BAOs. We have obtained results for $H_0$ and $Ω_{M}$ using GRBs+ SNe Ia+BAOs with better precision than the SNe Ia alone for every bin, thus confirming the beneficial role of BAOs and GRBs added together. In addition, consistent results between GRBs+ SNe Ia +BAOs are obtained when compared with the SNe Ia +BAOs, showing the importance of GRBs since the distance ladder is extended up to $z=5$ with a similar precision obtained with other probes without including the GRBs.

astro-ph.CO↗

arXiv2022

Optical and X-ray GRB Fundamental Planes as Cosmological Distance Indicators

Gamma-Ray Bursts (GRBs), can be employed as standardized candles, extending the distance ladder beyond Supernovae Type Ia (SNe Ia, $z=2.26$). We standardize GRBs using the 3D fundamental plane relation (the Dainotti relation) among the rest-frame end time of the X-ray plateau emission, its corresponding luminosity, and the peak prompt luminosity. Combining SNe Ia and GRBs, we constrain $Ω_{\text{M}}= 0.299 \pm 0.009$ assuming a flat $Λ$CDM cosmology with and without correcting GRBs for selection biases and redshift evolution. Using a 3D optical Dainotti correlation, we find this sample is as efficacious in the determination of $Ω_{\text{M}}$ as the X-ray sample. We trimmed our GRB samples to achieve tighter planes to simulate additional GRBs. We determined how many GRBs are needed as standalone probes to achieve a comparable precision on $Ω_{\text{M}}$ to the one obtained by SNe Ia only. We reach the same error measurements derived using SNe Ia in 2011 and 2014 with 142 and 284 simulated optical GRBs, respectively, considering the errorbars on the variables halved. These error limits will be reached in 2038 and in 2047, respectively. Using a doubled sample (obtained by future machine learning approaches allowing a lightcurve reconstruction and the estimates of GRB redhifts when z is unknown) compared to the current sample, with errorbars halved we will reach the same precision as SNe Ia in 2011 and 2014, now and in 2026, respectively. If we consider the current SNe precision, this will be reached with 390 optical GRBs by 2054.

astro-ph.CO↗

arXiv2022

PeV IceCube signals and $H_0$ tension in the framework of Non-Local Gravity

We study possible effects of non-local gravity corrections on the recent discovery by the IceCube collaboration reporting high-energy neutrino flux detected at energies of order PeV. Considering the 4-dimensional operator $\sim y_{αχ}\bar{L_{α}}\, H\, χ$, it is possible to explain both the IceCube neutrino rate and the abundance of Dark Matter, provided that non-local corrections are present in the cosmological background. Furthermore, the mechanism could constitute a natural way to address the $H_0$ tension issue.

hep-ph↗

arXiv2022

Model-independent reconstruction of $f(Q)$ non-metric gravity

We consider gravity mediated by non-metricity, with vanishing curvature and torsion. The gravitational action, including an arbitrary function of the non-metric scalar, is investigated in view of characterizing the dark energy effects. In particular, we present a method to reconstruct the $f(Q)$ action without resorting to \emph{a priori} assumptions on the cosmological model. To this purpose, we adopt a method based on rational Padé approximations, which provides a stable behaviour of the cosmographic series at high redshifts, alleviating the convergence issues proper of the standard approach. We thus describe how to reconstruct $f(Q)$ through a numerical inversion procedure based on the current observational bounds on cosmographic parameters. Our analysis suggests that the best approximation for describing the accelerated expansion of the universe is represented by a scenario with $f(Q)=α+βQ^{n}$. Finally, possible deviations from the standard $Λ$CDM model are discussed.

gr-qc↗

arXiv2022

Thermodynamic parametrization of dark energy

We propose a model-independent parametrization of dark energy motivated by thermodynamics. To this aim, we consider Padé polynomials to reconstruct the form of deceleration parameter adequate to describe different epochs of cosmic history and divergence-free in the far future. The proposed scenario also fulfills the demand of structure formation and contains the $Λ$CDM model as a limiting case. Thus, a numerical analysis at both background and perturbation levels is performed through the Markov Chain Monte Carlo method in view of the most recent cosmic data. We then use the observational constraints to explore the features of dark energy evolution and compare our findings with the predictions of the standard cosmological model.

astro-ph.CO↗

arXiv2022

Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies

In this paper we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant $H_0$, the $σ_8$--$S_8$ tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the $5.0\,σ$ tension between the {\it Planck} CMB estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade's experiments will be crucial. Moreover, we focus on the tension of the {\it Planck} CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the $H_0$--$S_8$ tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals.[Abridged]

astro-ph.CO↗

arXiv2022

Generalized McVittie geometry in Horndeski gravity with matter

We investigate McVittie and generalized McVittie solutions for Horndeski gravity with a spatially homogeneous gravitational scalar field, which is stealth at small scales near the central object but, at large scales, sources the FLRW universe in which the central inhomogeneity is embedded. Unlike previous studies, we include matter and obtain generalized McVittie solutions in the extended cuscuton model. The possible configurations are classified according to the time-dependence of the gravitational coupling, the radial energy flow, the accretion rate onto the central object, and the Hubble rate.

gr-qc↗

arXiv2022

Quasar standardization: Overcoming Selection Biases and Redshift Evolution

Quasars (QSOs) are extremely luminous active galatic nuclei currently observed up to redshift $z=7.642$. As such, they have the potential to be the next rung of the cosmic distance ladder beyond SNe Ia, if they can reliably be used as cosmological probes. The main issue in adopting QSOs as standard candles (similarly to Gamma-Ray Bursts) is the large intrinsic scatter in the relations between their observed properties. This could be overcome by finding correlations among their observables that are intrinsic to the physics of QSOs and not artifacts of selection biases and/or redshift evolution. The reliability of these correlations should be verified through well-established statistical tests. The correlation between the ultraviolet (UV) and X-ray fluxes developed by Risaliti \& Lusso is one of the most promising relations. We apply a statistical method to correct this relation for redshift evolution and selection biases. \textbf{Remarkably, we recover the the same parameters of the slope and the normalization as Risaliti \& Lusso. Our results establish the reliability of this relation, which is intrinsic to the QSO properties and not merely an effect of selection biases or redshift evolution. Hence,} the possibility to standardize QSOs as cosmological candles, thereby extending the Hubble diagram up to $z=7.54$.

astro-ph.HE↗