arXiv subjects

M. E. Rodrigues

Publications and source records attributed to M. E. Rodrigues.

At least 19 recordsLinked to original sources

arXiv2024

Most likely configurations for fermion localization in a Braneworld-$f(Q,B_Q)$

This study delves deeply into braneworld scenarios within modified gravity models, investigating their impact on particle localization and the structure of branes. Through a comprehensive blend of numerical analyses and theoretical inquiries, we unravel a nuanced correlation between deviations from standard General Relativity (GR) and the emergence of split branes. By employing probabilistic measurements, we pinpoint stable configurations that align with brane division intervals, thus challenging prevailing assumptions regarding the gravitational framework of our universe. Furthermore, our investigation extends to the localization of fermions within the brane, exposing intricate dynamics shaped by scalar field characteristics and modifications to gravitational models. By harnessing quantum information measurements, notably Shannon entropy, we discern heightened probabilities of fermion localization within the brane as gravitational models diverge from standard paradigms. This underscores the limitations of General Relativity in comprehensively describing the complexities inherent in our universe. Lastly, our exploration of massive fermions unveils their potential to breach the confines of the brane, hinting at promising avenues for future experimental endeavors aimed at probing the nature of extra dimensions and gravitational interactions. This suggests exciting prospects for advancing our understanding of fundamental physics beyond conventional boundaries.

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arXiv2024

Thermodynamics and Optical Properties of Phantom AdS Black Holes in Massive Gravity

Motivated by high interest in Lorentz invariant massive gravity models known as dRGT massive gravity, we present an exact phantom black hole solution in this theory of gravity and discuss the thermodynamic structure of the black hole in the canonical ensemble. Calculating the conserved and thermodynamic quantities, we check the validity of the first law of thermodynamics and the Smarr relation in the extended phase space. In addition, we investigate both the local and global stability of these black holes and show how massive parameters affect the regions of stability. We extend our study to investigate the optical features of the black holes such as the shadow geometrical shape, energy emission rate, and deflection angle. Also, we discuss how these optical quantities are affected by massive coefficients. Finally, we consider a massive scalar perturbation minimally coupled to the background geometry of the black hole and examine the quasinormal modes (QNMs) by employing the WKB approximation.

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arXiv2023

Topological phantom AdS black holes in $F(R)$ gravity

In this paper, we obtain exact phantom (A)dS black hole solutions in the context of $F(R)$ gravity with topological spacetime in four dimensions. Then, we study the effects of different parameters on the event horizon. In the following, we calculate the conserved and thermodynamic quantities of the system and check the first law of thermodynamics for these kinds of black holes. Next, we evaluate the local stability of the topological phantom (A)dS black holes in $F(R)$ gravity by studying the heat capacity and the geometrothemodynamic, where we show that the two approaches agrees. We extend our study and investigate global stability by employing the Gibbs potential and the Helmholtz free energy. In addition, the effects of different parameters on local and global stabilities will be highlighted.

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arXiv2016

Perfect fluid and F(T) gravity descriptions of inflationary universe and comparison with obervational data

We describe in this paper the observables of inflationary models, in particular the spectrum index of torsion scalar perturbations, the tensor-to-scalar ratio, and the running of the spectral index, in the framework of perfect fluid models and F(T) gravity theories through the reconstruction methods. Then, our results on the perfect fluid and F(T) gravity theories of inflation are compared with recent cosmological observations such as the Planck satellite and BICEP2 experiment. Ours studies prove that the perfect fluid and F(T) gravity models can reproduce the inflationary universe consistent above all with the Planck data. We have reconstructed several models and considered others which give the best fit values compatible with the spectral index of curvature perturbations, the tensor-to-scalar ratio, and the running of the spectral index within the allowed ranges suggested by the Planck and BICEP2 results.

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arXiv2016

Higher-Derivative $f(R,\Box R, T)$ Theories of Gravity

In literature there is a model of modified gravity in which the matter Lagrangian is coupled to the geometry via trace of the stress-energy momentum tensor $T=T_μ^μ$. This type of modified gravity is called as $f(R,T)$ in which $R$ is Ricci scalar $R=R_μ^μ$. We extend manifestly this model to include the higher derivative term $\Box R$. We derived equation of motion (EOM) for the model by starting from the basic variational principle. Later we investigate FLRW cosmology for our model. We show that de Sitter solution is unstable for a generic type of $f(R,\Box R, T)$ model. Furthermore we investigate an inflationary scenario based on this model. A graceful exit from inflation is guaranteed in this type of modified gravity.

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arXiv2015

Cosmological Evolution in f(R,T) theory with Collisional Matter

We study the evolution of the cosmological parameters, namely, the deceleration parameter $q(z)$ and the parameter of effective equation of state in a universe contains, besides the ordinary matter and dark energy, a self-interacting (collisional matter), in the generalized $f(R,T)$ theory of gravity, where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized FRW equations the equation of continuity and obtain a differential equation of second order in $H(z)$, and solve it numerically for studying the evolution of the cosmological parameters. Two $f(R,T)$ models are considered and the results with collisional matter are compared with the ones of the $Λ$CDM model, and also with the model where there exists only non-collisional matter. The curves show that the models are acceptable because the values found for $w_{eff}$ are consistent with the observational data.

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arXiv2015

Realistic f(T) model describing the de Sitter epoch of the dark energy dominated universe

We consider an exponential model within the so-called f(T) theory of gravity, where $T$ denotes the torsion scalar. We focus our work on a cosmological feature of such a model, checking whether it may describe the de Sitter stage of the current universe through the analysis of the redshift z. Our results shows that the model reproduces the de Sitter stage only for low-redshifts, where the perturbation function goes toward zero as the low values of the redshift are reached, whereas the effective parameter of equation of state goes to -1, which is the expected behavior for any model able to reproduce de Sitter stage.

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arXiv2015

Tolman-Oppenheimer-Volkoff Equations and their implications or the structures of relativistic Stars in f(T) gravity

We investigate in this paper the structures of neutron and quark stars in f(T) theory of gravity where T denotes the torsion scalar. Attention is attached to the TOV type equations of this theory and numerical integrations of these equations are performed with suitable EoS. We search for the deviation of the mass-radius diagrams for power-law and exponential type correction from the TT gravity. Our results show that for some values of the input parameters appearing in the considered models, f(T) theory promotes more the structures of the relativistic stars, in consistency with the observational data.

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arXiv2015

Geodesic Deviation Equation in $f (R,T)$ Gravity

In this paper, we investigate the modified Geodesic Deviation Equation (GDE) in the framework of $f(R,T)$ theory of gravity where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively, using the FLRW background. In this way, we obtain the GR equivalent (GDE) in $f(R,T)$ metric formalism. We also extend our work to the generalization of the Matting relation and perform the numerical analysis with GDE for null vector.

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arXiv2015

Spherically symmetric solutions of light Galileon

We have been studied the model of light Galileon with translational shift symmetry $ϕ\to ϕ+c$. The matter Lagrangian is presented in the form $\mathcal{L}_ϕ= -η(\partial ϕ)^2+βG^{μν}\partial_μϕ\partial_νϕ$. We have been addressed two issues: the first is that, we have been proven that, this type of Galileons belong to the modified matter-curvature models of gravity in type of $f(R,R^{μν}T_{μν}^m)$. Secondly, we have been investigated exact solution for spherically symmetric geometries in this model. We have been found an exact solution with singularity at $r=0$ in null coordinates. We have been proven that the solution has also a non-divergence current vector norm. This solution can be considered as an special solution which has been investigated in literature before, in which the Galileon's field is non-static (time dependence). Our scalar-shift symmetrized Galileon has the simple form of $ϕ=t$, which it is remembered by us dilaton field.

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arXiv2015

From the early to the late time universe within $f(T,\mathcal{T})$ gravity

In this paper we perform the reconstruction scheme of the gravitational action within $f(T,\mathcal{T})$ gravity, where $T$ and $\mathcal{T}$ denote the torsion scalar and the trace of the energy momentum tensor, respectively. We particularly focus our attention on the case where the algebraic function $f(T,\mathcal{T})$ is decomposed as a sum of two functions $f_1(T)$ and $f_2(\mathcal{T})$, i.e, $f(T,\mathcal{T})=f_{1}(T)+f_{2}(\mathcal{T})$. The description is essentially based on the scale factor and then, we consider two interesting and realistic expressions of this parameter and reconstruct the action corresponding to each phase of the universe. Our results show that some $f(T,\mathcal{T})$ models are able to describe the evolution of the universe from the inflation phase to the late time dark energy dominated phase.

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arXiv2015

Isotropic turbulence in the dark fluid universe with inhomogeneous equation of state

We investigate the turbulence effect in dark fluid universe with linear inhomogeneous equation of state. Attention is attached to two physical situations. First, we perform the perturbative analysis of turbulence and check its effects around the Big Rip. Later, treating the turbulence energy density as a part of total dark fluid, we study the stability of the system. The result shows that the stability is achieving as the energy density of turbulence decreases, changing into heat (the radiation), in perfect agreement with the avoidance of the Big Rip.

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arXiv2014

Bianchi type-I, type-III and Kantowski-Sachs solutions in f(T) gravity

In the context of modified tele-parallel theory of gravity, we undertake cosmological anisotropic models and search for their solutions. Within a suitable choice of non-diagonal tetrads, the decoupled equations of motion are obtained for Bianchi-I, Bianchi-III and Kantowski-Sachs models, from which we obtain the correspondent solutions. By the way, energy density and pressures are also obtained, showing, as an important result, that our universe may live a quintessence like universe even still anisotropic models are considered.

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arXiv2014

Cosmological viable f(R,T) dark energy model: dynamics and stability

In this paper we undertake the modified theory of gravity f(R,T) where R and T are the Ricci scalar and the trace of the energy momentum tensor, respectively. Imposing the conservation of the energy momentum tensor, we obtain a model about what dynamics and stability are studied. The stability is developed using the de Sitter and power-law solutions. The results show that the model presents stability for both the de Sitter and power-law solutions. Regarding the dynamics, cosmological solutions are obtained by integrating the background equations for both the low-redshift and High-redshift regimes and are consistent with the observational data.

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arXiv2013

LCDM Model in f(T) Gravity: Reconstruction, Thermodynamics and Stability

We investigate some cosmological features of the LCDM model in the framework of the generalized teleparallel theory of gravity f(T) where T denotes the torsion scalar. Its reconstruction is performed giving rise to an integration constant Q and other input parameters according to which we point out more analysis. Thereby, we show that for some values of this constant, the first and second laws of thermodynamics can be realized in the equilibrium description, for the universe with the temperature inside the horizon equal to that at the apparent horizon. Moreover, still within these suitable values of the constant, we show that the model may be stable using the de Sitter and Power-Law cosmological solutions.

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arXiv2013

Charged Black Holes in Generalized Teleparallel Gravity

In this paper we investigate charged static black holes in 4D for generalized teleparallel models of gravity, based on torsion as the geometric object for describing gravity according to the equivalence principle. As a motivated idea, we introduce a set of non-diagonal tetrads and derive the full system of non linear differential equations. We prove that the common Schwarzschild gauge is applicable only when we study linear f(T) case. We reobtain the Reissner-Nordstrom-de Sitter (or RN-AdS) solution for the linear case of f(T) and perform a parametric cosmological reconstruction for two nonlinear models. We also study in detail a type of the no-go theorem in the framework of this modified teleparallel gravity.

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arXiv2013

A Type of Levi-Civita's Solution in Modified Gauss-Bonnet Gravity

In this letter we obtain an exact solution for cylindrically symmetric modified Gauss Bonnet gravity. This metric is a generalization of the vacuum solution of the Levi-Civita in the general relativity. It describes an isotropic perfect fluid one parameter family of the gravitational configurations which can be interpreted as the exterior metric of a cosmic string. By setting the Gauss-Bonnet coupling parameter to zero, we recover the vacuum solution in the Einstein gravity as well.

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arXiv2013

Locally Rotationally Symmetric Bianchi Type-I cosmological model in $f(T)$ gravity: from early to Dark Energy dominated universe

We study the locally rotational symmetry Bianchi type-I dark energy model in the framework of $f(T)$ theory of gravity, where $T$ denotes the torsion scalar. A viable cosmological model is undertaken and the isotropization of this latter is checked, yielding a result that reflects the real evolution of our universe. Moreover, still in the anisotropic optic, a more complicated $f(T)$ model is obtained from the cosmological reconstruction scheme and the analysis shows that the universe is more anisotropic at the beginning if the terms of higher order in $T$ are not considered. This means that the non-linear model should be favoured by observational data.

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