Deceleration parameter

About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.

Anisotropic Bianchi-I Cosmological Model in String Cosmology with Variable Deceleration Parameter

Abstract: The present study deals with spatially homogeneous and anisotropic Bianchi type I cosmological model representing massive strings. The energy-momentum tensor, as formulated by Letelier [Phys. Rev. D 28, 2414 (1983)] has been used to construct massive string cosmological model for which we assume that the expansion scalar in the model is proportional to one of the components of shear tensor. The Einstein’s field equations have been solved by considering time dependent deceleration parameter which renders the scale factor a = (sinh(t )) 1 n, where and n are constants. It has been detected that, for n > 1, the presented model universe exhibits phase transition from early decelerated phase to accelerating phase at present epoch while for 0

Plane symmetric model in f ( R , T ) gravity

Abstract: A plane symmetric Bianchi-I model is explored in f(R, T) gravity, where R is the Ricci scalar and T is the trace of energy–momentum tensor. The solutions are obtained with the consideration of a specific Hubble parameter which yields a constant deceleration parameter. The various evolutionary phases are identified under the constraints obtained for physically viable cosmological scenarios. Although a single (primary) matter source is taken, due to the coupling between matter and f(R, T) gravity, an additional matter source appears, which mimics a perfect fluid or exotic matter. The solutions are also extended to the case of a scalar field model. The kinematical behavior of the model remains independent of f(R, T) gravity. The physical behavior of the effective matter also remain the same as in general relativity. It is found that f(R, T) gravity can be a good alternative to the hypothetical candidates of dark energy to describe the present accelerating expansion of the universe.

Holographic dark energy with the sign-changeable interaction term

Abstract: We use three infrared (IR) cutoffs, including the future event horizon, the Hubble and Granda–Oliveros (GO) cutoffs, to construct three holographic models of dark energy (DE) Additionally, we consider a Friedmann–Robertson–Walker (FRW) universe filled by a dark matter (DM) and a DE that interact with each other through a mutual sign-changeable interaction with positive coupling constant Thereinafter, we address the evolution of the some cosmological parameters, such as the equation of state (EoS) and dimensionless density parameters of DE as well as the deceleration parameter, during the cosmic evolution from the matter-dominated era until the late-time acceleration We observe that a holographic dark energy (HDE) model with Hubble cutoff interacting with DM cannot be in line with the current universe Our study shows that models with the future event horizon as the IR cutoff or the GO cutoff are in good agreement with the observational data In fact, we find out that these two recent models can predict the universe transition from a deceleration phase to the acceleration one in a compatible way with observations The three obtained models may also allow the EoS parameter to cross the phantom line, a result which depends on the values of the system’s constants such as the value of the interaction coupling constant

Exact Solutions of Bianchi Types $I$ and $V$ Models in $f(R,T)$ Gravity

Abstract: This paper is devoted to investigate the exact solutions of Bianchi types I and V spacetimes in the context of f(R, T) gravity [1]. For this purpose, we found two exact solutions in each case by using assumption of constant deceleration parameter and the variation law of Hubble parameter. The obtained solutions correspond to two different models of this universe. The physical behavior of these models is also discussed.

Bianchi type-III dark energy models with constant deceleration parameter in self-creation cosmology

Abstract: We have constructed dark energy cosmological models in an anisotropic Bianchi type-III space–time with a variable equation of state (EoS) parameter in Barber’s (Gen. Relativ. Gravitation, 14, 117, 1982) second self-creation theory of gravitation. Themodels are obtained using the special law of variation of Hubble’s parameter that yields a constant value of the deceleration parameter. In the two different models that we have obtained, the EoS parameter for dark energy is found to be time dependent. In one model the value of is in good agreement with the recent observations of type Ia supernovae (SNe Ia) data, SNe Ia data with cosmic microwave background radiation anisotropy and galaxy clustering statistics. Further we have discussed the well-known astrophysical phenomena, namely, the Hubble parameter H(z), luminosity distance dL, proper distance d(z), distance modulus (z), and look-back time with red shift. The expression for jerk parameter and statefinder parameters are also derived. PACS No.: 04.50.Kd. Resume : Nous construisons des modeles cosmologiques de l’energie sombre dans un espace–temps anisotrope de Bianchi de type III, dont l’equation d’etat (EoS) a un parametre variable dans une theorie de self-creation de la gravite de Barber (Gen. Relativ. Gravitation, 14, 117, (1982)). Les modeles sont obtenus grâce a la loi speciale de variation du parametre de Hubble qui donne une valeur constante au parametre de deceleration. Dans les deux modeles obtenus, nous trouvons une dependance temporelle au parametre de l’EoS pour l’energie sombre. Dans un desmodeles, la valeur de est en bon accord avec les recentes observations des donnees SNe Ia, des donnees SNe Ia avec anisotropie CMBR et la statistique des regroupements de galaxies. Nous analysons des quantites cosmologiques connues, comme le parametre de Hubble H(z), la distance de luminosite dL, la distance propre d(z), le module de distance (z) et la distance voyagee par la lumiere avec deplacement vers le rouge. Nous obtenons aussi les parametres d’etat (statefinders) et le parametre de sursaut cosmique (jerk). [Traduit par la Redaction]