Violation Of Strong Energy Condition Research Articles

Exact solutions based on Segre classification in the f(R) modified theory of gravity

In this article, the Segre classification approach is used to obtain some new solutions for spherically symmetric static spacetime metric corresponding to Segre types [(1, 111)], [1, (111)], [(1, 1)(11)], or [1, 1(11)]. The eigenvalue degeneracy in these situations correlates to timelike and spacelike eigenvectors and their primary null direction, which identify the kind of matter distribution in space and aid in the consideration of novel solutions for the corresponding energy momentum tensor. The isotropic Segre type [(1, 111)] in modified theory provides the Schwarzschild de-Sitter/anti-de-Sitter solutions, whereas in types [1, (111)] and [1, 1(11)] depending upon matter distribution new obtained solutions adhere all the physical conditions and present the viable trends of energy and causality conditions. Moreover, the profiles of the adiabatic index, surface, and gravitational redshift are observed along with the hydrostatic equilibrium using the Tolman–Oppenheimer–Volkoff equation. Additionally, for these types the solution is compared with observational data, and numerical values are calculated for central and surface densities and central pressure of compact star candidates KS1731-260\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$KS 1731-260$$\\end{document} and PSRJ1614-2230\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$PSR J1614-2230$$\\end{document}. Segre type [(1, 1)(11)] relates to a non-null electromagnetic field that corresponds to models with anisotropy in dark energy, which is demonstrated by graphical analysis. Dark energy does not behave as an ordinary matter resulting in the violation of strong energy condition and the causality condition.

Analyzing the geometrical and dynamical parameters of modified Teleparallel-Gauss–Bonnet model

To recreate the cosmological models, we employed the parametrization approach in modified teleparallel Gauss-Bonnet gravity. It has been interesting to apply the parametrization approach to investigate cosmological models. The real benefit of using this method is that the observational data may be incorporated to examine the cosmological models. Several cosmological parameters were examined, such as the Hubble parameter (H), the deceleration parameter (q), and the equation of state (EoS) parameter (w). The results obtained are consistent with recent cosmological findings in the conventional scenario. A transition scenario from a decelerating stage to an accelerating stage of cosmic evolution has been observed. The EoS parameter is also in the quintessence phase, which drives the accelerating expansion of the Universe. Also, we look at the violation of strong energy condition, which has become inevitable in the context of modified gravitational theory. Finally, we have performed the Om(z) diagnostic and also obtained the age of the Universe by using the data from the cosmological observations.

Accelerating cosmological models in f(T,B) gravitational theory

In this paper, we have explored the field equations of [Formula: see text] gravity as an extension of teleparallel gravity in an isotropic and homogeneous space-time. In the basic formalism developed, the dynamical parameters are derived by incorporating the power law and exponential scale factor function. The models show accelerating behavior and approach [Formula: see text]CDM at late time. The present value of the equation of state parameter for both the cases is obtained to be in accordance with the range provided by cosmological observations. The geometrical parameters and the scalar field reconstruction are performed to assess the viability of a late-time accelerating universe. Further, the stability of both the models is presented. It has been observed that both the models are parameter-dependent. Since most of the geometrically modified theories of gravity favor the violation of strong energy condition (SEC), we have derived the energy conditions both for the power law and exponential model. In both the models, the violation of SEC is established.

Rényi holographic dark energy models in teleparallel gravity

In this paper, we have investigated the physical behavior of cosmological models in the framework of modified teleparallel gravity. This model is established using a Rényi holographic dark energy (RHDE) model with a Hubble cut-off. Here, we have considered a homogeneous and isotropic Friedman universe filled with perfect fluid. The physical parameters are derived for the present model in compliances with 43 observational Hubble data sets. The equation-of-state parameter in terms of [Formula: see text] describes the transition of the universe between phantom and nonphantom phases in the context of [Formula: see text] gravity. Our model shows the violation of strong energy condition and the weak energy condition over the accelerated phantom regime. We also observed that these models occupy freezing regions through [Formula: see text]–[Formula: see text] plane. Consequently, our RHDE model is supported to the consequences of general relativity in the framework of [Formula: see text] modified gravity.

Bouncing cosmological model with general relativistic hydrodynamics in extended gravity

In this paper, in an extended theory of gravity, we have presented bouncing cosmological model at the backdrop of an isotropic, homogeneous space-time, in the presence of general relativistic hydrodynamics (GRH). The scale factor has been chosen in such a manner that with appropriate normalization, the quintom bouncing scenario can be assessed. Accordingly, the bounce occurs at [Formula: see text] and the corresponding Hubble parameter vanishes at the bounce epoch. The equation of state (EoS) parameter and the energy conditions of the model have been analyzed. The violation of strong energy condition further supports the behavior of extended gravity. As the bouncing cosmology suffers with instability, this model also shows the similar behavior.

Parameter Constrain of Nonminimal Derivative Coupling of Scalar Field Using Strong Energy Condition

The study aims to determine the constrain of the coupling parameter/xi of nonminimal derivative coupling theory (NMDC) of scalar field. The calculation of the parameter was build from the strong energy conditions combined to modified Einstein theory(i.e. the scalar filed act as the external source of gravity beside the ideal fluid). The violation of strong energy condition (SEC) indicate the atrracting gravity phenomenon. Then one can expecting two equations that consist of of energy density ρ and the momentum p, then one defined the deacceleration q to these equation. The present value of cosmological constant such as Hubble constant H, q, and scale factor a need to be put into the equations to determine the boundaries of the strong energ. The results show the coupling parameter must be ξ ≥ 1.2 × 1034 s2 for the SEC to be valid in the theory.

Transitioning Scenario of Bianchi-I Universe Within f (R,T) Formalism

In this paper, we report the existence of transitioning scenario of Bianchi type I universe in the context of $f\left(R,T\right)$ gravity with special case $f\left(R,T\right) = f_{1}(R) + f_{2}(R)f_{3}(T)$ and it's functional forms $f_{1}(R) = f_{2}(R) = R$ and $f_{3}(T) = \alpha T$ with $\alpha$ being constant. The exact solution of the Einstein's field equations are derived by using the generalized hybrid expansion law that yields the model of transitioning universe from early deceleration phase to current acceleration phase. Under this specification, we obtain the singular as well as non singular solution of Bianchi type I model depending upon the particular choice of the value of problem parameters. We also notice that the validation of weak energy condition and dominant energy condition and violation of strong energy condition occurs for these values of problem parameters. The deceleration parameter is found to be negative at present (z = 0) in the derived model which is supported by recent observations.

A study on the role of f(G) gravity on the emergent universe

Motivated by the recent work of Rastkar et al. (in Astrophys. Space Sci. 337:487, 2012) the present study has attempted to study the role of f(G) gravity in the emergent universe. Different energy conditions are examined for the effective energy density and violation of strong energy condition is observed. Also, the behavior of the equation of state parameter is studied for the effective energy density and dark energy density. It is found that the equation of state parameter behaves like phantom in both of the cases.

Ultrahigh energy particle collisions in a regular spacetime without black holes or naked singularities

We investigate here the particle acceleration and collisions with extremely large center of mass energies in a perfectly regular spacetime containing neither singularity nor an event horizon. The ultra-high energy collisions of particles near the event horizon of extremal Kerr blackhole, and also in many other examples of extremal blackholes have been investigated and reported recently. We studied an analogous particle acceleration process in the Kerr and Reissner-Nordstrom spacetimes without horizon, containing naked singularities. Further to this, we show here that the particle acceleration and collision process is in fact independent of blackholes and naked singularities, and can happen in a fully regular spacetime containing neither of these. We derive the conditions on the general static spherically symmetric metric for such a phenomena to happen. We show that in order to have ultra-high energy collisions it is necessary for the norm of the timelike Killing vector to admit a maximum with a vanishingly small but a negative value. This is also a condition implying the presence of a surface with extremely large but nevertheless finite value of the redshift or blueshift. Conditions to have ultrahigh energy collisions and regular center imply the violation of strong energy condition near the center while the weak energy condition is respected in the region around the center. Thus the central region is surrounded by a dark energy fluid. Both the energy conditions are respected at the location where the high energy collisions take place. As a concrete example we then investigate the acceleration process in the spacetime geometry derived by Bardeen which is sourced by a non-liner self-gravitating magnetic monopole.

Cosmology with x-matter

Motivated by the possibility of $H_0t_0 > 1$ where $H_0$ and $t_0$ are the Hubble parameter and the age of the universe, respectively, we investigate the cosmology including x-matter. x-matter is expressed by the equation of state $p_x=w_0\rho_{x0} + c_s^2(\rho_x-\rho_{x0})$, where $p_x$, $\rho_x$ and $\rho_{x0}$ are the pressure, the density of x-matter and the density at present, respectively. $w_0$ and $c_s^2$ are functions of $\rho_x$ in general. x-matter has the most general form of the equation of state which is characterized by 1)violation of strong energy condition at present for $w_0 < -1/3$ ; 2) locally stable (i.e. $c_s^2\geq 0$); 3)causality is guaranteed ($c_s\leq 1$). Considering the case that $w_0$ and $c_s^2$ are constants, we find that there is a large parameter space of $(w_0,c_s^2,\Omega_{x0})$ in which the model universe is consistent with the age of the universe and the observations of distant Type I supernovae.