arXiv subjects

Bruno J. Barros

Publications and source records attributed to Bruno J. Barros.

17 recordsLinked to original sources

arXiv2026

Scaling solutions in three-form cosmology

A hybrid three-form model of dark energy is developed in order to identify scaling solutions, a long-sought feature in three-form cosmology. Exploiting Hodge dualities, the theory is formulated in terms of two scalar functions that are associated with the conjugate momentum, and the three-form dual vector in an isotropic background. The resulting Lagrangian yields a stable scaling attractor where the three-form energy density tracks the dominant background fluid. A dynamical mechanism is also identified that naturally drives the system out of this regime toward a late-time accelerated phase distinguishable from a cosmological constant. This constitutes the first realization of scaling behavior within a three-form dark energy framework.

astro-ph.CO↗

arXiv2025

Vector wormholes as conduits for matter interaction

In this work, we focus on the dynamics of a massive one-form field, \textbf{B}, often referred to simply as a vector field, that is minimally coupled to standard Einstein gravity. In the framework of four-dimensional spacetimes, the theory of a massive one-form propagates three massive vector degrees of freedom. The inclusion of a self-interacting potential in this theory results in the breaking of gauge invariance. The breaking of such a fundamental symmetry in Classical Electromagnetism may introduce a ghost mode in massive vector theories, which generally leads to their instability. However, in the context of wormhole physics, the existence of at least one ghost degree of freedom turns out to be a necessary condition to support these exotic geometries within effective field theories. This requirement serves as a strong motivation for our work, wherein we explore the role and phenomenology of massive one-forms, minimally coupled to Einstein gravity, in providing the necessary conditions to sustain wormhole spacetimes. We further analyze the coupling of matter fields to such a vector field through conformal couplings and explore their impact on energy conditions and the physical viability of wormhole solutions.

gr-qc↗

arXiv2025

Non-canonical 3-form dark energy

In this study, we meticulously construct a 3-form Lagrangian designed to mimic the dynamics of both dust matter in the past and dark energy driving the acceleration in the present era. A dynamical systems approach is used to investigate the underlying behavior of the cosmological background. By investigating the influence of the potential slope and initial conditions on the dynamical solutions, we identify distinct viable scenarios capable of replicating a De Sitter universe in the present epoch. An intriguing aspect of the model is the existence of solutions describing multiple inflationary phases in which the 3-form self-interacting potential decays rapidly.

gr-qc↗

arXiv2024

Non-trivial thick brane realisations with 3-forms

We explore the construction of four-dimensional thick branes supported by massless 3-forms in a five-dimensional bulk space. The required residual Poincaré symmetry on the brane is realised as a combination of the bulk symmetries and the internal gauge symmetry of the 3-form. We show the presence of a gradient instability for the perturbations orthogonal to the brane when its profile decays slowly in the asymptotic regions. In particular, we ascertain that the prevailing profiles found in the literature are susceptible to such instabilities. We confirm our results by transitioning to the dual formulation in terms of a shift-symmetric scalar. In this formulation, the residual Poincaré group is trivially realised without internal symmetries, and there is a diagonal translational invariance in the fifth dimension reminiscent of the invariance under translations orthogonal to the brane of the dual 3-form. We demonstrate the extension of our results to the cases of de Sitter and Anti de Sitter branes where the gradient instabilities of asymptotically slowly decaying branes persist. Finally, we briefly comment on the construction of thick branes with massive 3-forms and their 1-form duals.

gr-qc↗

arXiv2023

Wormholes with matter haunted by conformally coupled ghosts

In this work, we present novel analytical solutions for static and spherically symmetric wormhole geometries threaded by an anisotropic distribution of matter conformally coupled to a scalar ghost field. We explore the main features of the theory, such as the dynamics of the scalar field and matter throughout the wormhole, as well as the role played by the non-minimal coupling. Furthermore, coupled ghosts in the presence of a scalar potential are considered and traversability conditions are analysed within such geometrical scheme. More specifically, we find analytical solutions that although the energy density of the ghost is strictly negative, the energy density of matter may attain positive values.

gr-qc↗

arXiv2023

Coupling quintessence kinetics to electromagnetism

We propose a general model where quintessence couples to electromagnetism via its kinetic term. This novelty generalizes the linear dependence of the gauge kinetic function on $ϕ$, commonly adopted in the literature. The interaction naturally induces a time variation of the fine-structure constant that can be formulated within a disformally coupled framework, akin to a Gordon metric. Through a suitable parametrization of the scalar field and the coupling function, we test the model against observations sensitive to the variation of $α$. We undertake a Bayesian analysis to infer the free parameters with data from Earth based, astrophysical and early Universe experiments. We find that the evolution of $α$ is specific to each cosmological era and slows down at late times when dark energy accelerates the Universe. While the most stringent bound on the interaction is obtained from atomic clocks measurements, the quasars provide a constraint consistent with weak equivalence principle tests. This promising model is to be further tested with upcoming and more precise astrophysical measurements, such as those of the ESPRESSO spectrograph.

astro-ph.CO↗

arXiv2023

Is there evidence for CIDER in the Universe?

In this work we analyze the full linear behaviour of the constrained interacting dark energy (CIDER) model, which is a conformally coupled quintessence model tailored to mimic a $Λ$CDM expansion. We compute the matter and temperature anisotropies power spectra and test the model against recent observational data. We shed light on some particular subtleties of the background behaviour that were not fully captured in previous works, and study the physics of the linear cosmological observables. One novelty found was that matter perturbations are enhanced at large scales when compared with the ones of the standard $Λ$CDM. The reason and impact of this trend on the cosmological observables and on the physics of the early Universe are considered. We find that the introduction of the coupling parameter alleviates the $σ_8$ tension between early and late time probes although Planck data favours the $Λ$CDM limit of the model.

astro-ph.CO↗

arXiv2022

Dissecting kinetically coupled quintessence: phenomenology and observational tests

We investigate an interacting dark energy model which allows for the kinetic term of the scalar field to couple to dark matter via a power-law interaction. The model is characterised by scaling solutions at early times, which are of high interest to alleviate the coincidence problem, followed by a period of accelerated expansion. We discuss the phenomenology of the background evolution and of the linear scalar perturbations and we identify measurable signatures of the coupling in the dark sector on the cosmic microwave background, the lensing potential auto-correlation and the matter power spectra. We also perform a parameter estimation analysis using data of cosmic microwave background temperature, polarisation and lensing, baryonic acoustic oscillations and supernovae. We find that the strength of the coupling between the dark sectors, regulated by the parameter $α$, is constrained to be of order $10^{-4}$. A model selection analysis does not reveal a statistical preference between $Λ$CDM and the Kinetic model.

astro-ph.CO↗

arXiv2021

Static spherically symmetric three-form stars

We consider interior static and spherically symmetric solutions in a gravity theory that extends the standard Hilbert-Einstein action with a Lagrangian constructed from a three-form field $A_{αβγ}$, which generates, via the field strength and a potential term, a new component in the total energy-momentum tensor of the gravitational system. We formulate the field equations in Schwarzschild coordinates and investigate their solutions numerically for different equations of state of neutron and quark matter, by assuming that the three field potential is either a constant or possesses a Higgs-like form. Moreover, stellar models, described by the stiff fluid, radiation-like, bag model and the Bose-Einstein condensate equations of state are explicitly obtained in both general relativity and three-form gravity, thus allowing an in-depth comparison between the astrophysical predictions of these two gravitational theories. As a general result we find that for all the considered equations of state, three-form field stars are more massive than their general relativistic counterparts. As a possible astrophysical application of the obtained results, we suggest that the 2.5$M_{\odot}$ mass compact object, associated with the GW190814 gravitational wave event, could be in fact a neutron or a quark star described by the three-form field gravity theory.

gr-qc↗

arXiv2020

Black hole and naked singularity geometries supported by three-form fields

We investigate static and spherically symmetric solutions in a gravity theory that extends the standard Hilbert-Einstein action with a Lagrangian constructed from a three-form field $A_{αβγ}$, which is related to the field strength and a potential term. The field equations are derived from a variational principle and are obtained explicitly for a static and spherically symmetric geometry in vacuum. For the case of the vanishing three-form field potential the gravitational field equations can be solved exactly. However, for arbitrary potentials, due to their mathematical complexity, numerical approaches are adopted in studying the behavior of the metric functions and the three-form field. To this effect, the field equations are reformulated in a dimensionless form and are solved numerically by introducing a suitable independent radial coordinate. We detect the formation of a black hole from the presence of a Killing horizon for the time-like Killing vector in the metric tensor components. Several models, corresponding to different functional forms of the three-field potential, namely, the Higgs and exponential type, are considered. In particular, naked singularity solutions are also obtained for the exponential potential case. Finally, the thermodynamic properties of these black hole solutions, such as the horizon temperature, specific heat, entropy and evaporation time due to the Hawking luminosity, are also investigated in detail.

gr-qc↗

arXiv2020

Bouncing cosmology in $f(R,\mathcal{G})$ gravity by order reduction

A bouncing universe is a viable candidate to solve the initial singularity problem. Here we consider bouncing solutions in the context of $f(R,\mathcal{G})$ gravity by using an order reduction technique which allows one to find solutions that are perturbatively close to General Relativity. This procedure also acts as a model selection approach. Indeed, several covariant gravitational actions leading to a bounce are directly selected by demanding that the Friedmann equation derived within such gravity theories coincides with the one emerging from Loop Quantum Cosmology.

gr-qc↗

arXiv2020

Testing $F(Q)$ gravity with redshift space distortions

A Bayesian statistical analysis using redshift space distortions data is performed to test a model of Symmetric Teleparallel Gravity where gravity is non-metrical. The cosmological background mimics a $Λ$CDM evolution but differences arise in the perturbations. The linear matter fluctuations are numerically evolved and the study of the growth rate of structures is analysed in this cosmological setting. The best fit parameters reveal that the $σ_8$ tension between Planck and Large Scale Structure data can be alleviated within this framework.

gr-qc↗

arXiv2020

Spherical collapse in coupled quintessence with a $Λ$CDM background

In this work we study the growth of cold dark matter density perturbations in the nonlinear regime on a conformally coupled quintessence model in which the background is designed to mimic a $Λ$CDM cosmology. The spherical collapse of overdense regions is analyzed. We highlight the role of the coupling on the overall dynamics, trace the evolution of the density contrast throughout the cosmic history and compute perturbative parameters such as the critical density contrast. We find that the coupling has the influence of delaying the collapse due to the slower growth of matter perturbations. We follow to compute the cluster number counts using the Press-Schechter and Sheth-Tormen mass functions. In both cases, the transfer of energy between the dark energy field and dark matter suppresses the number of objects at low redshifts and enhances the number at high redshifts. Finally, we compute the expected cluster number counts for the future eROSITA mission and the current South Pole Telescope survey.

astro-ph.CO↗

arXiv2019

Kinetically coupled dark energy

The main goal of this work is to propose a generalized model of interacting dark energy which allows for the kinetic term of a scalar field to couple to the matter species a priori in the action. We derive the modified field equations, and present novel cosmological solutions for a specific coupled model. One alluring consequence is the emergence of solutions allowing for an early scaling regime, possible due to two novel critical points, followed by a period of accelerated expansion. Using a dynamical system analysis, we show that the presence of the coupling may alter the dynamical nature of the critical points and can be used to enlarge the existence and stability regions of these. Using constraints from Planck data we are able to find an upper bound on the coupling parameter. Finally, it is shown how this theory encapsulates a wide variety of dark energy models already present in the literature.

gr-qc↗

arXiv2019

Coupled quintessence with a $Λ$CDM background: removing the $σ_8$ tension

A well-known problem of the $Λ$CDM model is the tension between the relatively high level of clustering, as quantified by the parameter $σ_8$, found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. In this paper we show that coupled quintessence, i.e. a single dark energy scalar field conformally coupled to dark matter through a constant coupling, can solve this problem if the background is taken to be identical to the $Λ$CDM one. We show that two competing effects arise. On one hand, the additional scalar force is attractive, and is therefore expected to increase the clustering. On the other, in order to obtain the same background as $Λ$CDM, coupled quintessence must have a smaller amount of dark matter near the present epoch. We show that the second effect is dominating today and leads to an overall slower growth. Comparing to redshift distortion data, we find that coupled quintessence with $Λ$CDM background solves the tension between early and late clustering. We find for the coupling $β$ and for $σ_8$ the best fit values $|β| = 0.079^{+ 0.059}_{- 0.067}$ and $σ_8 = 0.818^{+0.115}_{-0.088}$. These values also fit the lensing data from the KiDS-450 survey. We also estimate that the future missions SKA and Euclid will constrain $β$ with an error of $\pm\, 1.5\times10^{-3}$ and for $σ_8$ of $\pm \,1.8\times10^{-3}$ at $1σ$ level.

astro-ph.CO↗

arXiv2018

Wormhole geometries supported by three-form fields

In this work, we find novel static and spherically symmetric wormhole geometries using a three-form field. By solving the gravitational field equations, we find a variety of analytical and numerical solutions and show that it is possible for the matter fields threading the wormhole to satisfy the null and weak energy conditions throughout the spacetime, when the three-form field is present. In these cases, the form field is responsible for supporting the wormhole and all the exoticity is confined to it. Thus, the three-form curvature terms, which may be interpreted as a gravitational fluid, sustain these non-standard wormhole geometries, fundamentally different from their counterparts in General Relativity. We also show that in the case of a vanishing redshift function the field can display a cosmological constant behavior.

gr-qc↗

arXiv2015

3-form inflation in Randall-Sundrum II

It has been shown in the last few years that 3-form fields present viable cosmological solutions for inflation and dark energy with particular observable signatures distinct from those of canonical single scalar field inflation. The aim of this work is to explore the dynamics of a single 3-form in five dimensional Randall-Sundrum II braneworld scenario, in which a 3-form is confined to the brane and only gravity propagates in the bulk. We compare the solutions with the standard four dimensional case already studied in the literature. In particular, we evaluate how the spectral index and the ratio of tensor to scalar perturbations are influenced by the presence of the bulk and put constraints on the parameters of the models in the light of the recent Planck 2015 data.

astro-ph.CO↗