arXiv subjects

Ines G. Salako

Publications and source records attributed to Ines G. Salako.

15 recordsLinked to original sources

arXiv2025

Slow-roll Natural & Hilltop Inflation in Rastall Gravity

This study provides a concise analysis of inflation under Rastall gravity by examining three types of potential such as the power law, natural, and hilltop potentials. Choosing a minimal interaction between matter and gravity, we derived the modified slow-roll parameters, the scalar spectral index $(n_s)$, the tensor spectral index $(n_T)$, and the tensor-to-scalar ratio $(r)$. For a general power-law potential as well as for Natural & Hilltop inflation, we calculated these quantities and subsequently plotted their trajectories in the $(n_s, r)$ plane. For the power-law potential, only the cases $n = 2/3$ and $n = 1$ satisfy the observational constraint of the Planck 2018 data. The natural potential analysis shows that the mass scale is crucial, with better compatibility achieved at $f = 5M_{p}$ compared to $f = 10M_{p}$. Lastly, the Hilltop potential results indicate that among the cases studied $m = 3/2, 2, 3$, and $4$, only $m = 3/2$ exhibits marginal consistency with observational bounds, while the other cases fail to produce acceptable $(n_s - r)$ trajectories.

gr-qc↗

arXiv2021

Compact stellar models in modified gravity

In the present investigation compact stellar models are dealt with in the framework of the modified gravity theory, specifically of $f(\mathbb{T},\mathcal{T})$ type. We have considered that the compact objects are following a spherically symmetric static metric and obtained the Einstein field equations in the spacetime of $f(\mathbb{T},\mathcal{T})$. To make the Einstein equations solvable we employ the methodology of conformal Killing vectors. Thereafter by using the MIT bag equation of state to the compact stars, considering that the stars are formed by strange quark, we find the solutions set. The solutions are examined via several physical tastings which exhibit viability of the model.

gr-qc↗

arXiv2020

Rip cosmologies, Wormhole Solutions and Big Trip in the $f(T,\mathcal{T})$ theory of gravity

Rip cosmological models have been investigated in the framework of $f(T,\mathcal{T})$ theory of gravity, where $T$ denotes the torsion and $\mathcal{T}$ is the trace of the energy-momentum tensor. These phantom cosmological models revealed that at initial epoch a EoS parameter $ω<-1$ and tends asymptotically at late phase to $-1$ $(ω\rightarrow -1)$. On the other hand, Wormhole Solutions and Big Trip have been subject of an investigation. The wormhole throat radius $R(t)$ and the conditions to be satisfied so that produces the Big Trip phenomenon have been discussed.

gr-qc↗

arXiv2019

Reconstructing $f(T)$ modified gravity from ECHDE and ECNADE models

We investigate alternative candidates to dark energy that can explain the current state of the universe in the framework of the generalized teleparallel theory of gravity $f(T)$ where $T$ denotes the torsion scalar. To achieve this, we carried out a series of reconstruction taking into account to the ordinary and entropy-corrected versions of the holographic and new agegraphic dark energy models. These models used as alternative to dark energy in the literature in order describe the current state of our universe. It is remarked that the models reconstructed indicates behaviors like phantom or quintessence models. Furthermore, we also generated the EoS parameters associated to entropy-corrected models and we observed a transition phase between quintessence state and phantom state as showed by recent observational data. We also investigated on the stability theses models and we created the $\{r-s\}$. The behavior of certains physical parameters as speed of sound and the Statefinder parameters are compatible with current observational data.

physics.gen-ph↗

arXiv2019

$4$-index theory of gravity and its relation with the violation of the energy-momentum conservation law

Recently, a $4$-index generalization of the Einstein theory is proposed by Moulin (Eur. Phys. J. C 77, 878 (2017)). Using this method, we find the most general $2$-index field equations derivable from the Einstein-Hilbert action. The application of Newtonian limit, the role of gravitational coupling constant and the effects of the properties of ordinary energy-momentum tensor in obtaining a $4$-index gravity theory have been studied. We also address the results of building Weyl free $4$-index gravity theory. Our study displays that both the Einstein and Rastall theories can be obtained as the subclasses of a $4$-index gravity theory which shows the power of $4$-index method in unifying various gravitational theories. It is also obtained that the violation of the energy-momentum conservation law may be allowed in $4$-index gravity theory, and moreover, the contraction of $4$-index theory generally admits a non-minimal coupling between geometry and matter field in the Rastall way. This study also shows that, unlike the Einstein case, the gravitational coupling constant of $4$-index Rastall theory generally differs from that of the ordinary $2$-index Rastall theory.

physics.gen-ph↗

arXiv2018

Implications of the Generalized Entropy Formalisms on the Newtonian Gravity and Dynamics

Employing the Verlinde's hypothesis, and considering two well-known generalized entropy formalisms, two modifications to the Newtonian gravity are derived. In addition, it has been shown that the generalized entropy measures may also provide theoretical basis for the Modified Newtonian Dynamics (MOND) theory and generate its modified forms. Since these entropy measures are also successful in describing the current accelerated universe, our results indicate that the origin of dark sectors of cosmos may be unified to meeting the generalized entropy measures instead of the Boltzmann-Gibbs entropy by the gravitational systems due to the long-range nature of gravity.

physics.gen-ph↗

arXiv2017

Thin-Shell Wormholes in Neo-Newtonian Theory

In this paper, we constructed an acoustic thin-shell wormhole (ATW) under neo-Newtonian theory using the Darmois-Israel junction conditions. To determine the stability of the ATW by applying the cut-and-paste method, we found the surface density and surface pressure of the ATW under neo-Newtonian hydrodynamics just after obtaining an analog acoustic neo-Newtonian solution. We focused on the effects of the neo-Newtonian parameters by performing stability analyses using different types of fluids, such as a linear barotropic fluid (LBF), a Chaplygin fluid (CF), a logarithmic fluid (LogF), and a polytropic fluid (PF). We showed that a fluid with negative energy is required at the throat to keep the wormhole stable. The ATW can be stable if suitable values of the neo-Newtonian parameters $ς$, $A$, and $B$ are chosen.

gr-qc↗

arXiv2017

A Generalization to the Rastall Theory and Cosmic Eras

A generalized version for the Rastall theory is proposed showing the agreement with the cosmic accelerating expansion. In this regard, a coupling between geometry and the pressureless matter fields is derived which may play the role of dark energy responsible for the current accelerating expansion phase. Moreover, our study also shows that the radiation field may not be coupled to the geometry in a non-minimal way which represents that the ordinary energy-momentum conservation law is respected by the radiation source. It is also shown that the primary inflationary era may be justified by the ability of the geometry to couple to the energy-momentum source in an empty flat FRW universe. In fact, this ability is independent of the existence of the energy-momentum source and may compel the empty flat FRW universe to expand exponentially. Finally, we consider a flat FRW universe field by a spatially homogeneous scalar field evolving in potential $\mathcal{V}(ϕ)$, and study the results of applying the slow-roll approximation to the system which may lead to an inflationary phase for the universe expansion.

gr-qc↗

arXiv2016

Thermodynamic analysis of the static spherically symmetric field equations in Rastall theory

The restrictions on the Rastall theory due to apply the Newtonian limit to the theory are derived. In addition, we use the zero-zero component of the Rastall field equations as well as the unified first law of thermodynamics to find the Misner-Sharp mass content confined to the event horizon of the spherically symmetric static spacetimes in the Rastall framework. The obtained relation is calculated for the Schwarzschild and de-Sitter back holes as two examples. Bearing the obtained relation for the Misner-Sharp mass in mind together with recasting the one-one component of the Rastall field equations into the form of the first law of thermodynamics, we obtain expressions for the horizon entropy and the work term. Finally, we also compare the thermodynamic quantities of system, including energy, entropy and work, with their counterparts in the Einstein framework to have a better view about the role of the Rastall hypothesis on the thermodynamics of system.

gr-qc↗

arXiv2016

Aspects of Some New Versions of Pilgrim Dark Energy in DGP Braneworld

The illustration of cosmic acceleration under two interacting dark energy models (pilgrim dark energy with Granda and Oliveros cutoff and its generalized ghost version) in DGP braneworld framework is presented. In the current scenario, the equation of state parameter, deceleration parameter, $ω_{D}-ω'_{D}$ plane and statefinder diagnosis are investigated. The equation state parameter behave-like phantom era of the universe. The deceleration parameter depicts the accelerated expansion of the universe in both models. The cosmological planes like $ω_{D}-ω'_{D}$ and statefinder corresponds to $Λ$CDM limit. To end, we remark that our results support to phenomenon of pilgrim dark energy and cosmic acceleration. Also, the results are consistent with observational data.

gr-qc↗

arXiv2016

Generalized Mattig's relation in Brans-Dicke-Rastall gravity

The Geodesic Deviation Equation is being studied in Brans-Dicke-Rastall gravity. We briefly discuss the Brans-Dicke-Rastall gravity and then construct GDE for FLRW metric. In this way, the obtained geodesic deviation equation will correspond to the Brans-Dicke-Rastall gravity. Eventually, we solve numerically the null vector GDE to obtain from Mattig relation, the deviation vector $η(z)$ and observer area distance $r_0(z)$ and compare the results with $Λ$CDM model.

gr-qc↗

arXiv2016

Reconstruction, Thermodynamics and Stability of $Λ$CDM Model in $f(T,\mathcal{T})$ Gravity

We reconstruct the $Λ$CDM model for $f(T,\mathcal{T})$ Theory, where $T$ is the torsion scalar and $\mathcal{T}$ the trace of the energy-momentum tensor. The result shows that the action of $Λ$CDM is a combination of a linear term, a constant ($-2Λ$) and a non-linear term given by the product $\sqrt{-T}F_g\left[(T^{1/3}/16πG)\left(16πG\mathcal{T}+T+8Λ\right)\right]$, with $F_g$ being a generic function. We show that to maintain conservation of energy-momentum tensor should impose that $F_g[y]$ must be linear on the trace $\mathcal{T}$. This reconstruction decays in the $f(T)$ Theory for $F_g\equiv Q$, with $Q$ a constant. Our reconstruction describes the cosmological eras to the present time. The model present stability within the geometric and matter perturbations for the choice $F_g=y$, where $y=(T^{1/3}/16πG)\left(16πG\mathcal{T}+T+8Λ\right)$, except for geometric part to de Sitter model. We impose the first and second laws of thermodynamics to the $Λ$CDM and find the condition where they are satisfied, that is, $T_A,G_{eff}>0$, however where this is not possible for cases where we choose, leading to a breakdown of positive entropy and Misner-Sharp energy.

gr-qc↗

arXiv2015

Geodesic Deviation Equation in $Λ$CDM $f(T,\mathcal{T})$ gravity

The geodesic deviation equation has been investigated in the framework of $f(T,\mathcal{T})$ gravity, where $T$ denotes the torsion and $\mathcal{T}$ is the trace of the energy-momentum tensor, respectively. The FRW metric is assumed and the geodesic deviation equation has been established following the General Relativity approach in the first hand and secondly, by a direct method using the modified Friedmann equations. Via fundamental observers and null vector fields with FRW background, we have generalized the Raychaudhuri equation and the Mattig relation in $f(T,\mathcal{T})$ gravity. Furthermore, we have numerically solved the geodesic deviation equation for null vector fields by considering a particular form of $f(T,\mathcal{T})$ which induces interesting results susceptible to be tested with observational data.

gr-qc↗

arXiv2015

$f(T,\mathcal{T})$ Cosmological Models in Phase Space

In this paper we explore $f(T, \mathcal{T})$, where $T$ and $\mathcal{T}$ denote the torsion scalar and the trace of the energy-momentum tensor respectively. We impose the covariant conservation to the energy-momentum tensor and obtain a cosmological $f(T, \mathcal{T})$ respectively. We impose the covariant conservation to the energy-momentum tensor and obtain a cosmological $f(T, \mathcal{T})$ model. Then, we study the stability of the obtained model for power-law and de Sitter solutions and our result show that the model can be stable for some values of the input parameters, for both power-law and de Sitter solutions.

physics.gen-ph↗

arXiv2015

Holographic dark energy reconstruction of $f(T,\mathcal{T})$ gravity

The present paper reports a holographic reconstruction scheme for $f(T,\mathcal T)$ gravity proposed in Harko et al. $\emph{JCAP}\; 12(2014)021$ where $T$ is the torsion scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor considering future event horizon as the enveloping horizon of the universe. We have considered $f(T, \mathcal T)=T + γg(\mathcal T)$ and $f(T,\mathcal T) =β\mathcal T + g(T)$ for reconstruction. We observe that the derived $f(T,\mathcal T)$ models can represent phantom or quintessence regimes of the universe which are compatible with the current observational data.

gr-qc↗