The Mimetic Matter in LRS Bianchi Type-I Model

This paper deals with the Locally rotationally symmetric (LRS) Bianchi type-I universe model in Mimetic Gravity Theory assuming it an extended form of General Relativity Theory. It was proclaimed as a conformal transformation of the Einstein-Hilbert action from Einstein frame to Jordon frame. At the outset, we have proposed a potential function on account of clarifying the expansion of our universe by considering the general solutions of the field equations that originate from the action of the theory including the Lagrange multipliers. Lastly, after having been achieved the general equation of the state parameter ω, we discussed whether the result corresponds to some fluids illuminating the expansion of the Universe or not.

Scalar fields in f(G) gravity

In this study, we investigated scalar field in [Formula: see text]-gravity by using LRS Bianchi type-I universe. Massless and massive scalar field models are separately constructed in [Formula: see text]-gravity. Massless scalar field models are examined in the cases of constant and exponential potential fields. For all models, solutions of field equations are obtained under the consideration of [Formula: see text]. [Formula: see text] functions for each model are separately attained in theory. It is shown that constructed models in the presence of massless scalar field permit quintessence scalar field. Also, it is observed that each model indicates expanding universe with deceleration. Also, kinematical quantities are analyzed in the light of obtained solutions. All models are concluded with a geometric and physical perspective.

Probing kinematics and fate of Bianchi type I universe in Brans–Dicke theory

In this paper, we examine the existence of Bianch type I Brans–Dicke universe by performing statistical test from [Formula: see text] and SN Ia observational data sets. We find that anisotropic Brans-Dicke ([Formula: see text] BD) model provides a reasonable fit with observational data. In addition to [Formula: see text], we also use Akaike information creation (AIC) and Bayes information creation (BIC) to determine the values of best fit parameters. The model under consideration represents a transitioning universe from early decelerating phase to current accelerating phase. We obtain the present age of the universe as 13.732 Gyrs, which is in good agreement with WMAP observations. The physical behavior of particle horizon and [Formula: see text] parameter of the derived model are also discussed.

Scalar field solutions for anisotropic universe models in various gravitation theories

In this study, we have investigated homogeneous and anisotropic Marder and Bianchi type I universe models filled with normal and phantom scalar field matter distributions with [Formula: see text] in [Formula: see text] gravitation theory (T. Harko et al., Phys. Rev. D 84 (2011) 024020). In this model, [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. To obtain exact solutions of modified field equations, we have used anisotropy feature of the universe and different scalar potential models with [Formula: see text] function. Also, we have obtained general relativity (GR) solutions for normal and phantom scalar field matter distributions in Marder and Bianchi type I universes. Additionally, we obtained the same scalar function values by using different scalar field potentials for Marder and Bianchi type I universe models with constant difference in [Formula: see text] gravity and GR theory. From obtained solutions, we get negative cosmological term value for [Formula: see text] constant scalar potential model with Marder and Bianchi type I universes in GR theory. These results agree with the studies of Maeda and Ohta, Aktaş et al. also Biswas and Mazumdar. Finally, we have discussed and compared our results in gravitation theories.

Effects of anisotropy on the sign-changeable interacting Tsallis holographic dark energy

We consider a spatially homogeneous and anisotropic Bianchi type-I universe which is filled by pressureless dark matter (DM) and Tsallis holographic dark energy (THDE). We assume the two dark components of the universe are interacting with each other throughout a sign-changeable mutual interaction term. Various infra-red (IR) cutoffs are studied, and it is obtained that all models display classical instability by themselves at the future [Formula: see text]. Moreover, we find out that some models can cross the phantom line. In order to have a more comprehensive study, the statefinder diagnostic and the [Formula: see text] plane are also investigated showing that the model parameters significantly affect the evolution trajectories in the [Formula: see text] and [Formula: see text] planes.

Intermediate inflation with non-canonical scalar field in the low anisotropy Universe

The behavior of a non-canonical scalar field within an anisotropic Bianchi type I, spatially homogeneous Universe in the framework of the intermediate inflation will be studied. It will be examined on the condition that both the anisotropy and non-canonical sources come together if there is any improvement in compatibility with the observational data originated from Planck 2015. Based on this investigation, it can be observed that automatically a steep potential which can manage inflation in a better way will be obtained. Additionally, as a common procedure for an inflationary study, we shall try to calculate the related inflationary observables such as the amplitude of the scalar perturbations, scalar and tensor spectral indices, tensor-to-scalar ratio, the running spectral index and the number of e-folds. As an exciting part of our results, we will find that our model has a good consistency compared to data resulting from CMB and different Planck results. To justify our claims, the well-known canonical inflationary scenario in an anisotropic Bianchi type I Universe will also be evaluated.

The late cosmic acceleration and the coincidence problem in Bianchi type I Universe

In locally rotationally symmetric (LRS) Bianchi-I spacetime, we are considering a special kind of a scale factor, called the hybrid expansion law (HEL). The HEL provides a description of the transition from deceleration to cosmic acceleration. A non-minimal interaction between dark energy (DE) and dark matter (DM) allows to combine the transition from matter dominance to the era of the DE dominance with the transition from decelerated to accelerated expansion. In the proposed model, the linear interaction of the two components solves the coincidence problem of our present Universe. We present examples of numerical values of the HEL parameters compatible with the constructed model and the observational data.

Stability of the Universe Model Coupled with Phantom and Tachyon Fields

In this paper, we study the phase space analysis of locally rotationally symmetric Bianchi type I universe model by taking interactions between dark matter and scalar field models. We define normalized dimensionless variables to develop an autonomous system of equations. We also find the corresponding critical points in order to study the dynamics of the system. The dynamical analysis indicates that all the critical points correspond to accelerated cosmic expansion for tachyon coupled field. We observe that positive values of m provide more stable future attractors as compared to its negative values. We also analyze the behavior of power-law scale factor which shows different cosmological phases. It is found that the region for decelerated expansion gets larger for the phantom coupled matter by increasing m while this region decreases for tachyon coupled field.