arXiv subjects

Antonella Cid

Publications and source records attributed to Antonella Cid.

15 recordsLinked to original sources

arXiv2025

Could a thin-shell configuration lie hidden within the Universe?

This article explores the cosmological scenario in which our Universe contains a hidden thin-shell configuration. We investigate a degenerate modification of the Friedmann-Robertson-Walker metric obtained through a coordinate transformation applied to the radial coordinate, analogous to recent approaches that address the Big Bang singularity via spacetime defects. The resulting metric, while formally satisfying the standard homogeneous Friedmann equations, actually describes an evolving wormhole geometry with two asymptotically flat Friedmann-Robertson-Walker regions connected by a throat located at the coordinate singularity. Using Israel's junction formalism, we demonstrate that this coordinate singularity corresponds to a thin shell characterized by exotic matter with well-defined surface energy density and isotropic pressure. The shell obeys the barotropic equation of state $p = -\rho/2$, confirming the presence of exotic matter that violates the standard energy condition, which is a requirement for maintaining wormhole geometries. As the universe expands, this thin shell becomes increasingly diluted, scaling as $1/a(t)$ with the cosmic scale factor.

gr-qc↗

arXiv2023

Modified holographic Ricci interacting dark energy models: dynamical system analysis and bayesian comparison

We perform a dynamical system analysis and a Bayesian model selection for a new set of interacting scenarios in the framework of modified holographic Ricci dark energy models (MHR-IDE). The dynamical analysis shows a modified radiation epoch and a late-time attractor corresponding to dark energy. We use a combination of background data such as type Ia supernovae, cosmic chronometers, cosmic microwave background, and baryon acoustic oscillations measurements. We find evidence against all the MHR-IDE scenarios studied with respect to $Λ$CDM, when the full joint analysis is considered.

gr-qc↗

arXiv2022

Dynamics and statefinder analysis of a class of sign-changeable interacting dark energy scenarios

We revise the dynamical properties of a class of cosmological models where the dark sector interacts through an interacting term that changes sign during evolution. In particular, we obtain the critical points and we investigate the existence and stability conditions for cosmological solutions, describing radiation, matter and dark energy dominated eras. We find that all the studied models admit a stable critical point corresponding to an accelerated phase. We use background data to find the best fit parameters for one of the studied models, resulting an interacting parameter with a definite sign within $1σ$ confidence level, consistent with the results of the dynamical system analysis. We also compute the statefinder parameters and plot the $r-q$ and $r-s$ planes, where we observe different trajectories when we vary the interaction parameter for a specific model and when we vary the interacting scenario. We can in this sense distinguish among models, including $Λ$CDM.

astro-ph.CO↗

arXiv2020

Bayesian Comparison of Interacting Modified Holographic Ricci Dark Energy Scenarios

We perform a Bayesian model selection analysis for interacting scenarios of dark matter and modified holographic Ricci dark energy (MHRDE) with linear interacting terms. We use a combination of some of the latest cosmological data such as type Ia supernovae, cosmic chronometers, cosmic microwave background and baryon acoustic oscillations measurements. We find strong evidence against all the MHRDE interacting scenarios studied with respect to $Λ$CDM when the full joint analysis is considered.

astro-ph.CO↗

arXiv2019

Modelling the current accelerated expansion of the Universe with Holographic Dark Energy

In this work we explore a Holographic Dark Energy Model in a flat Friedmann-Lemaître-Robertson-Walker Universe, which contains baryons, radiation, cold dark matter and dark energy within the framework of General Relativity. Furthermore, we consider three types of phenomenological interactions in the dark sector. With the proposed model we obtained the algebraic expressions for the cosmological parameters of our interest: the deceleration and coincidence parameters. Likewise, we graphically compare the proposed model with the $Λ$CDM model.

gr-qc↗

arXiv2019

Bayesian Comparison of Interacting Scenarios

We perform a Bayesian model selection analysis for different classes of phenomenological coupled scenarios of dark matter and dark energy with linear and non-linear interacting terms. We use a combination of some of the latest cosmological data such as type Ia supernovae (SNe Ia), cosmic chronometers (CC), cosmic microwave background (CMB) and two sets of baryon acoustic oscillations measurements, namely, 2-dimensional angular measurements (BAO2) and 3-dimensional angle-averaged measurements (BAO3). We find weak and moderate evidence against two-thirds of the interacting scenarios considered with respect to $Λ$CDM when the full joint analysis is considered. About one-third of the models provide a description to the data as good as the one provided by the standard model. Our results also indicate that either SNe Ia, CC or BAO2 data by themselves are not able to distinguish among interacting models or $Λ$CDM but the standard BAO3 measurements and the combination with the CMB data are indeed able to discriminate among them. We find that evidence disfavoring interacting models is weaker when we use BAO2 (data claimed to be almost model-independent) instead of the standard BAO3 measurements. These results help select classes of viable and non-viable interacting models in light of current data.

astro-ph.CO↗

arXiv2019

On sign-changeable interaction in FLRW cosmology

We investigate an interacting two-fluid model in a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) Universe, when the energy transfer between these two dark components is produced by a factorisable nonlinear sign-changeable interaction depending linearly on the energy density and quadratically on the deceleration parameter. We solve the source equation and obtain the effective energy densities of the dark sector and their components. We show that the effective equation of state of the dark sector includes some of the several kind of Chaplygin gas equations of state as well as a generalization of the polytropic equation of state. We use bayesian statistics methods to constrain free parameters in the models during its most recent evolution considering supernovae type Ia and measurements of the Hubble expansion rate. The resulting constraints provide new information on sign-changeable interactions, its equivalences and compatibility with previous models and novel late time universe dynamics.

gr-qc↗

arXiv2018

Non-minimally coupled scalar field cosmology with torsion

In this work we present a generalized Brans-Dicke lagrangian including a non-minimally coupled Gauss-Bonnet term without imposing the vanishing torsion condition. In the resulting field equations, the torsion is closely related to the dynamics of the scalar field, i.e., if non-minimally coupled terms are present in the theory, then the torsion must be present. For the studied lagrangian we analyze the cosmological consequences of an effective torsional fluid and we show that this fluid can be responsible for the current acceleration of the universe. Finally, we perform a detailed dynamical system analysis to describe the qualitative features of the model, we find that accelerated stages are a generic feature of this scenario.

gr-qc↗

arXiv2017

AIC and BIC for cosmological interacting scenarios

In this work we study linear and non-linear cosmological interactions, which depend on dark matter and dark energy densities in the framework of General Relativity. By using the Akaike information criterion (AIC) and the Bayesian information criterion (BIC) with data from SnIa (Union 2.1 and binned JLA), H(z), BAO and CMB we compare the interacting models among themselves and analyze whether more complex interacting models are favored by these criteria. In this context, we find some suitable interactions that alleviate the coincidence problem.

astro-ph.CO↗

arXiv2016

Cosmic anisotropic doomsday in Bianchi type I universes

In order to investigate if the anisotropy of the spacetime may induce future singularities at a finite value of the cosmic time on the evolution of cosmological models, we study vacuum and non-vacuum Bianchi type I spacetimes exhibiting such future singularities. We show that in the case of Kasner vacuum cosmologies the spacetime may rip itself apart in a finite time, and only in the direction corresponding to the unique scale factor which diverges at this finite value of the cosmic time. The other two directional scale factors and the average scale factor do not diverge and tend to zero at this time, while the directional and average expansion rates also become infinite. Due to the absence of the matter content this anisotropic future singularity is induced by the shear scalar, which also blows up at this time. We call such a singularity "Vacuum Rip". For non-vacuum solutions we discuss fully anisotropic Bianchi type I spacetimes filled with a stiff fluid and ellipsoidal (axisymmetric) cosmological models filled with matter with isotropic and anisotropic barotropic pressure, and characterized by $σ/θ=const$, where $σ$ and $θ$ are the shear scalar and the expansion scalar respectively.

gr-qc↗

arXiv2016

Intermediate accelerated solutions as generic late-time attractors in a modified Jordan-Brans-Dicke theory

We investigate a Jordan-Brans-Dicke (JBD) scalar field, $Φ$, with power-law potential in the presence of a second scalar field, $ϕ$, with an exponential potential, in both the Jordan and the Einstein frames. We present the relation of our model with the induced gravity model with power-law potential and the integrability of this kind of models is discussed when the quintessence field $ϕ$ is massless, and has a small velocity. We prove that in JBD theory, the de Sitter solution is not a natural attractor but an intermediate accelerated solution of the form $a(t)\simeq e^{α_1 t^{p_1}}$, as $t\rightarrow \infty$ where $α_1>0$ and $0 0$ and $0<p_2<1$, for the same conditions on the parameters as in the Jordan frame. In the special case of a quadratic potential in the Jordan frame, or for a constant potential in the Einstein's frame, these solutions are of saddle type. Finally, we present a specific elaboration of our extension of the induced gravity model in the Jordan frame, which corresponds to a linear potential of $Φ$. The dynamical system is then reduced to a two dimensional one, and the late-time attractor is linked with the exact solution found for the induced gravity model. In this example the intermediate accelerated solution does not exist, and the attractor solution has an asymptotic de Sitter-like evolution law for the scale factor. Apart from some fine-tuned examples such as the linear, and quadratic potential ${U}(Φ)$ in the Jordan frame, it is true that intermediate accelerated solutions are generic late-time attractors in a modified JBD theory.

gr-qc↗

arXiv2015

On the consistency of tachyon warm inflation with viscous pressure

We obtain conditions for the existence of an attractor in the system of equations describing a tachyon warm inflationary model with bulk viscosity taken into account. When these conditions are met the evolution approaches slow-roll regime. We present the primordial power spectrum for the tachyon field by considering a dissipation coefficient depending on the scalar field and temperature.

gr-qc↗

arXiv2012

Intermediate Inflation in the Jordan-Brans-Dicke Theory

We present an intermediate inflationary stage in a Jordan-Brans-Dicke theory. In this scenario we analyze the quantum fluctuations corresponding to adiabatic and isocurvature modes. The model is compared to that described by using the intermediate model in Einstein General Relativity theory. We assess the status of this model in light of the WMAP7 data.

astro-ph.CO↗

arXiv2012

Observational constraints on a cosmological model with Lagrange multipliers

Cosmological models with Lagrange multipliers are appealing because they could explain the behaviour of the dark sector in a unified way. In this work we analyse extensions to the "Dust of Dark Energy model" proposed in arXiv:1003.5751 by including spatial curvature and more general potentials of the scalar field. We perform dynamical system analysis and we determine the evolution of the equation of state parameter as a function of the scale factor. We present observational constraints on this model by using Union2.1 dataset and H(z) data.

astro-ph.CO↗

arXiv2011

Constraints from CMB in the intermediate Brans-Dicke inflation

We study an intermediate inflationary stage in a Jordan-Brans-Dicke theory. In this scenario we analyze the quantum fluctuations corresponding to adiabatic and isocurvature modes. Our model is compared to that described by using the intermediate model in Einstein general relativity theory. We assess the status of this model in light of the seven-year WMAP data.

astro-ph.CO↗