arXiv subjects

Jailson S. Alcaniz

Publications and source records attributed to Jailson S. Alcaniz.

At least 19 recordsLinked to original sources

arXiv2024

Testing the isotropy of cosmic acceleration with Pantheon+ and SH0ES: A cosmographic analysis

We use a recent Pantheon+SH0ES compilation of Type Ia Supernova distance measurements at low-redshift, i.e., $0.01 \leq z \leq 0.10$, in order to investigate the directional dependency of the deceleration parameter ($q_0$) in different patches ($60^{\circ}$ size) across the sky, as a probe of the statistical isotropy of the Universe. We adopt a cosmographic approach to compute the cosmological distances, fixing $H_0$ and $M_B$ to reference values provided by the collaboration. By looking at 500 different patches randomly taken across the sky, we find a maximum $\sim 3σ$ CL anisotropy level for $q_0$, whose direction points orthogonally to the cosmic microwave background (CMB) dipole axis, i.e., $(RA^{\rm SN},DEC^{\rm SN}) = (267^{\circ},6^{\circ})$ vs $(RA^{\rm CMB},DEC^{\rm CMB}) = (167^{\circ},-7^{\circ})$. We assessed the statistical significance of those results, finding that such a signal is expected due to the limitations of the observational sample. These results support that there is no significant evidence for a departure from the cosmic isotropy assumption, one of the pillars of the standard cosmological model.

astro-ph.CO↗

arXiv2024

Forecasting constraints on the baryon mass fraction in the IGM from fast radio bursts and type Ia supernovae

Fast Radio Bursts (FRBs) are millisecond transient radio events with a high energy. By identifying the origin of the \textbf{burst}, it is possible to measure the redshift of the host galaxy, which can be used to constrain cosmological and astrophysical parameters and test aspects of fundamental physics when combined with the dispersion measure ($DM$). However, some factors limit the cosmological application of FRBs: (i) the poor modelling of the fluctuations in the $DM$ due to spatial variation in the cosmic electrons density; (ii) the fact that the fraction of baryon mass in the intergalactic medium ($f_{IGM}$) is degenerated with some cosmological parameters; (iii) the limited knowledge about host galaxy contribution ($DM_{host}$). In this work, we investigate the impact of different redshift distribution models of FRBs to constrain the baryon fraction in the IGM and host galaxy contribution. We use a cosmological model-independent method developed in previous work \cite{Lemos2023} to perform the analysis and combine simulated FRB data from Monte Carlo simulation and supernovae data. We assume four distribution models for the FRBs: gamma-ray bursts (GRB), star formation rate (SFR), uniform and equidistant (ED). Also, we consider samples with $N = 15, 30, 100$ and $500$ points and different values of the fluctuations of electron density in the $DM$, $δ= 0, 100, 200, 400, 230\sqrt{z}$ pc/cm$^{3}$. Our analysis shows that all the distribution models present consistent results within $2σ$ for the free parameters $f_{IGM}$ and $DM_{host,0}$ and highlights the crucial role of $DM$ fluctuations in obtaining more precise measurements.

astro-ph.CO↗

arXiv2023

Cosmological model-independent constraints on the baryon fraction in the IGM from fast radio bursts and supernovae data

Fast Radio Bursts (FRBs) are millisecond-duration radio transients with an observed dispersion measure ($DM$) greater than the expected Milky Way contribution, which suggests that such events are of extragalactic origin. Although some models have been proposed to explain the physics of the pulse, the mechanism behind the FRBs emission is still unknown. From FRBs data with known host galaxies, the redshift is directly measured and can be combined with estimates of the $DM$ to constrain the cosmological parameters, such as the baryon number density and the Hubble constant. However, the poor knowledge of the fraction of baryonic mass in the intergalactic medium ($f_{IGM}$) and its degeneracy with the cosmological parameters impose limits on the cosmological application of FRBs. In this work we present a cosmological model-independent method to determine the evolution of $f_{IGM}$ combining the latest FRBs observations with localized host galaxy and current supernovae data. We consider constant and time-dependent $f_{IGM}$ parameterizations and show, through a Bayesian model selection analysis, that a conclusive answer about the time-evolution of $f_{IGM}$ depend strongly on the $DM$ fluctuations due to the spatial variation in cosmic electron density ($δ$). In particular, our analysis show that the evidence varies from strong (in favor of a growing evolution of $f_{IGM}$ with redshift) to inconclusive, as larger values of $δ$ are considered.

astro-ph.CO↗

arXiv2022

The Hubble Constant Troubled by Dark Matter in Non-Standard Cosmologies

The Standard Cosmological Model has experienced tremendous success at reproducing observational data by assuming a universe dominated by a cosmological constant and dark matter in a flat geometry. However, several studies, based on local measurements, indicate that the universe is expanding too fast, in disagreement with the Cosmic Microwave Background. Taking into account combined data from CMB, Baryon Acoustic Oscillation, and type Ia Supernovae, we show that if the mechanism behind the production of dark matter particles has at least a small non-thermal origin, one can induce larger values of the Hubble rate $H_0$, within the $Λ$CDM, to alleviate the trouble with $H_0$. In the presence of non-standard cosmology, however, we can fully reconcile CMB and local measurements and reach $H_0=70-74\, {\rm km s^{-1} Mpc^{-1}}$.

astro-ph.CO↗

arXiv2021

Discrepancy between cosmological and electroweak observables in Higgs Inflation

In this work, we revisit the non-minimally coupled Higgs Inflation scenario and investigate its observational viability in light of the current Cosmic Microwave Background, Baryon Acoustic Oscillation and type Ia Supernovae data. We explore the effects of the Coleman-Weinberg approximation to the Higgs potential in the primordial universe, connecting the predictions for the Lagrangian parameters at inflationary scales to the electroweak observables through Renormalization Group methods at two-loop order. As the main result, we find that observations on the electroweak scale are in disagreement with the constraints obtained from the cosmological data sets used in the analysis. Specifically, an $\approx 8σ$-discrepancy between the inflationary parameters and the electroweak value of the top quark mass is found, which suggests that a significant deviation from the scenario analysed is required by the cosmological data.

hep-ph↗

arXiv2020

Is there evidence for a hotter Universe?

The measurement of present-day temperature of the Cosmic Microwave Background (CMB), $T_0 = 2.72548 \pm 0.00057$ K (1$σ$), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, $H_0$, obtained from measurements of the CMB temperature fluctuations assuming the standard $Λ$CDM model exhibit a large ($4.1σ$) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in $T_0$ could alleviate or solve the $H_0$-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift $T(z)$ measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of $\gtrsim 1.9σ$ from the $T_0$ values required to solve the $H_0$ tension. This result reinforces the idea that a solution of the $H_0$-tension problem in fact requires either a better understanding of the systematic errors on the $H_0$ measurements or new physics.

astro-ph.CO↗

arXiv2019

Revisiting the statistical isotropy of GRB sky distribution

The assumption of homogeneity and isotropy on large scales is one of the main hypotheses of the standard cosmology. In this paper, we test the hypothesis of isotropy from the two-point angular correlation function of 2626 gamma-ray bursts (GRB) of the FERMI GRB catalogue. We show that the uncertainties in the GRB positions induce spurious anisotropic signals in their sky distribution. However, when such uncertainties are taken into account no significant evidence against the large-scale statistical isotropy is found. This result remains valid even for the sky distribution of short-lived GRB, contrarily to previous reports.

astro-ph.CO↗

arXiv2019

J-PAS: forecasts on dark energy and modified gravity theories

The next generation of galaxy surveys will allow us to test one of the most fundamental assumptions of the standard cosmology, i.e., that gravity is governed by the general theory of relativity (GR). In this paper we investigate the ability of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) to constrain GR and its extensions. Based on the J-PAS information on clustering and gravitational lensing, we perform a Fisher matrix forecast on the effective Newton constant, $μ$, and the gravitational slip parameter, $η$, whose deviations from unity would indicate a breakdown of GR. Similar analysis is also performed for the DESI and Euclid surveys and compared to J-PAS with two configurations providing different areas, namely an initial expectation with 4000 $\mathrm{deg}^2$ and the future best case scenario with 8500 $\mathrm{deg}^2$. We show that J-PAS will be able to measure the parameters $μ$ and $η$ at a sensitivity of $2\% - 7\%$, and will provide the best constraints in the interval $z = 0.3 - 0.6$, thanks to the large number of ELGs detectable in that redshift range. We also discuss the constraining power of J-PAS for dark energy models with a time-dependent equation-of-state parameter of the type $w(a)=w_0+w_a(1-a)$, obtaining $Δw_0=0.058$ and $Δw_a=0.24$ for the absolute errors of the dark energy parameters.

astro-ph.CO↗

arXiv2019

How does an incomplete sky coverage affect the Hubble Constant variance?

We address the $\simeq 4.4σ$ tension between local and the CMB measurements of the Hubble Constant using simulated Type Ia Supernova (SN) data-sets. We probe its directional dependence by means of a hemispherical comparison through the entire celestial sphere as an estimator of the $H_0$ cosmic variance. We perform Monte Carlo simulations assuming isotropic and non-uniform distributions of data points, the latter coinciding with the real data. This allows us to incorporate observational features, such as the sample incompleteness, in our estimation. We obtain that this tension can be alleviated to $3.4σ$ for isotropic realizations, and $2.7σ$ for non-uniform ones. We also find that the $H_0$ variance is largely reduced if the data-sets are augmented to 4 and 10 times the current size. Future surveys will be able to tell whether the Hubble Constant tension happens due to unaccounted cosmic variance, or whether it is an actual indication of physics beyond the standard cosmological model.

astro-ph.CO↗

arXiv2019

Looking for interactions in the cosmological dark sector

We study observational signatures of non-gravitational interactions between the dark components of the cosmic fluid, which can be either due to creation of dark particles from the expanding vacuum or an effect of the clustering of a dynamical dark energy. In particular, we analyse a class of interacting models ($Λ$(t)CDM), characterised by the parameter $α$, that behaves at background level like cold matter at early times and tends to a cosmological constant in the asymptotic future. In our analysis we consider both background and primordial perturbations evolutions of the model. We use Cosmic Microwave Background (CMB) data together with late time observations, such as the Joint Light-curve Analysis (JLA) supernovae data, the Hubble Space Telescope (HST) measurement of the local value of the Hubble-Lemaître parameter, and primordial deuterium abundance from Ly$α$ systems to test the observational viability of the model and some of its extensions. We found that there is no preference for values of $α$ different from zero (characterising interaction), even if there are some indications for positive values when the minimal $Λ$(t)CDM model is analysed. When extra degrees of freedom in the relativistic component of the cosmic fluid are considered, the data favour negative values of $α$, which means an energy flux from dark energy to dark matter.

astro-ph.CO↗

arXiv2019

Variation in the fine-structure constant, distance-duality relation and the next generation of high-resolution spectrograph

The possibility of variation of the fundamental constants of nature has been a long-standing question, with important consequences for fundamental physics and cosmology. In particular, it has been shown that variations in the fine-structure constant, $α$, are directly related to violation of the distance duality relation (DDR), which holds true as long as photons travel on unique null geodesics and their number is conserved. In this paper we use the currently available measurements of ${Δα}/α$ to impose the most stringent constraints on departures of the DDR to date, here quantified by the parameter $η$. We also perform a forecast analysis to discuss the ability of the new generation of high-resolution spectrograph, like ESPRESSO/VLT and E-ELT-HIRES, to constrain the DDR parameter $η$. From the current data we obtain constraints on $η$ of the order of $10^{-7}$ whereas the forecasted constraints are two orders of magnitude lower. Considering the expected level of uncertainties of the upcoming measurements, we also estimate the necessary number of data points to confirm the hypotheses behind the DDR.

astro-ph.CO↗

arXiv2019

Primordial gravitational waves and the H0-tension problem

We analyse the H0-tension problem in the context of models of the early universe that predict a blue tilted spectrum of primordial gravitational waves (GW's). By considering the GW's contribution, Neff^GW, to the effective number of relativistic degrees of freedom, Neff, and assuming standard particle physics, we discuss the effects of Neff^GW on the background expansion, especially the constraints on the Hubble parameter H0. We analyse three scenarios which take into account the contribution of Neff^GW and perform a statistical study using recent data of cosmic microwave background, baryon acoustic oscillation, the latest measurement of the local expansion rate, along with the LIGO constraints on the tensor to scalar ratio and the tensor index. For the models explored, we show that an additional contribution from the primordial GW's background to Neff does not solve but alleviate the current H0-tension problem.

astro-ph.CO↗

arXiv2018

A Model-independent Test of Cosmic Isotropy with Low-z Pantheon Supernovae

The assumption of homogeneity and isotropy on large scales is one of the main hypotheses of the standard cosmological model. In this paper, we revisit a test of cosmological isotropy using type Ia supernova (SN Ia) distances provided by the latest SN Ia compilation available, namely, the Pantheon compilation. We perform a model-independent analysis by selecting low-redshift subsamples lying in two redshift intervals, i.e., z $\leq$ 0.10 and z $\leq$ 0.20. By mapping the directional asymmetry of cosmological parameters across the sky, we show that the current SN Ia data favor the hypothesis of cosmic isotropy, as the anisotropy found in the maps can be mostly ascribed to the nonuniform sky coverage of the data rather than an actual cosmological signal. These results confirm that there is null evidence against the cosmological principle in the low-redshift universe.

astro-ph.CO↗

arXiv2018

The $H_0$ and $σ_8$ tensions and the scale invariant spectrum

In a previous communication we showed that a joint analysis of Cosmic Microwave Background (CMB) data and the current measurement of the local expansion rate favours a model with a scale invariant spectrum (HZ) over the minimal $Λ$CDM scenario provided that the effective number of relativistic degrees of freedom, $N_{eff}$, is taken as a free parameter. Such a result is basically obtained due to the Hubble Space Telescope (HST) value of the Hubble constant, $H_0 = 73.24 \pm 1.74$ $\rm{km.s^{-1}.Mpc^{-1}}$ (68\% C.L.), as the CMB data alone discard the HZ+$N_{eff}$ model. Although such a model is not physically motivated by current scenarios of the early universe, observations pointing to a scale invariant spectrum may indicate that the origin of cosmic perturbations lies in an unknown physical process. Here, we extend the previous results performing a Bayesian analysis using joint CMB, HST, and Baryon Acoustic Oscillations (BAO) measurements. In order to take into account the well-known tension on the value of the fluctuation amplitude parameter, $σ_8$, we also consider Cluster Number counts (CN) and Weak Lensing (WL) data. We use two different samples of BAO data, which are obtained using two-point spatial (BAO 2PCF) and angular (BAO 2PACF) correlation functions. Our results show that a joint CMB+HST+BAO 2PCF analysis discards the HZP$+N_{eff}$ model with respect to the minimal $Λ$CDM scenario whereas the combination CMB+HST+BAO 2PACF favours the former model, even when an extended dataset with NC and WL is considered.

astro-ph.CO↗

arXiv2018

Screening mechanisms in hybrid metric-Palatini gravity

We investigate the efficiency of screening mechanisms in the hybrid metric-Palatini gravity. The value of the field is computed around spherical bodies embedded in a background of constant density. We find a thin shell condition for the field depending on the background field value. In order to quantify how the thin shell effect is relevant, we analyze how it behaves in the neighborhood of different astrophysical objects (planets, moons or stars). We find that the condition is very well satisfied except only for some peculiar objects. Furthermore we establish bounds on the model using data from solar system experiments such as the spectral deviation measured by the Cassini mission and the stability of the Earth-Moon system, which gives the best constraint to date on $f(R)$ theories. These bounds contribute to fix the range of viable hybrid gravity models.

gr-qc↗

arXiv2018

Observational constraints on Gauss-Bonnet cosmology

We analyze a fully geometric approach to dark energy in the framework of $F(R,{\cal G})$ theories of gravity, where $R$ is the Ricci curvature scalar and ${\cal G}$ is the Gauss-Bonnet topological invariant. The latter invariant naturally exhausts, together with $R$, the whole curvature content related to curvature invariants coming from the Riemann tensor. In particular, we study a class of $F(R, {\cal G})$ models with power law solutions and find that, depending on the value of the geometrical parameter, a shift in the anisotropy peaks position of the temperature power spectrum is produced, as well as an increasing in the matter power spectrum amplitude. This fact could be extremely relevant to fix the form of the $F(R, {\cal G})$ model. We also perform a MCMC analysis using both Cosmic Microwave Background data by the Planck (2015) release and the Joint Light-Curve Analysis of the SNLS-SDSS collaborative effort, combined with the current local measurements of the Hubble value, $H_0$, and galaxy data from the Sloan Digital Sky Survey (BOSS CMASS DR11). We show that such a model can describe the CMB data with slightly high $H_0$ values, and the prediction on the amplitude matter spectrum value is proved to be in accordance with the observed matter distribution of the universe. At the same time, the value constrained for the geometric parameter implies a density evolution of such a components that is growing with time.

gr-qc↗

arXiv2018

Dynamical analysis on $f(R,\mathcal{G})$ cosmology

We use a dynamical system approach to study the cosmological viability of $f(R,\mathcal{G})$ gravity theories. The method consists of formulating the evolution equations as an autonomous system of ODEs, using suitable variables. The formalism is applied to a class of models in which $f(R,\mathcal{G})\propto R^{n}\mathcal{G}^{1-n}$ and its solutions and corresponding stability are analysed in detail. New accelerating solutions that can be attractors in the phase space are found. We also find that this class of models does not exhibit a matter-dominated epoch, a solution which is inconsistent with current cosmological observations.

gr-qc↗

arXiv2017

Strong energy condition and the repulsive character of f(R) gravity

The Raychaudhuri equation enables to examine the whole spacetime structure without specific solutions of Einstein's equations, playing a central role for the understanding of the gravitational interaction in Cosmology. In General Relativity, without considering a cosmological constant, a non-positive contribution in the Raychaudhuri equation is usually interpreted as the manifestation of the attractive character of gravity. In this case, particular energy conditions -- indeed the strong energy condition -- must be assumed in order to guarantee the attractive character. In the context of f(R) gravity, however, even assuming the standard energy conditions one may have a positive contribution to the Raychaudhuri equation. Besides providing a simple way to explain the observed cosmic acceleration, this fact opens the possibility of a repulsive character of this kind of gravity. In order to discuss physical bounds on f(R) models, we address the attractive/non-attractive character of f(R) gravity considering the Raychaudhuri equation and assuming the strong energy condition along with recent estimates of the cosmographic parameters.

gr-qc↗