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

2019 ◽  
Vol 34 (29) ◽  
pp. 1950239 ◽  
Author(s):  
Ruslan K. Muharlyamov ◽  
Tatiana N. Pankratyeva
Keyword(s):  
Special Kind ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Type I ◽  
Coincidence Problem ◽  
Linear Interaction ◽  
Proposed Model ◽  
Rotationally Symmetric ◽  
Present Universe ◽  
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.

scholarly journals Could the Lyra manifold be the hidden source of the dark energy?

2017 ◽  
Vol 14 (04) ◽  
pp. 1750063 ◽  
Author(s):  
Kangujam Priyokumar Singh ◽  
Mahbubur Rahman Mollah
Keyword(s):  
Dark Energy ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Type I ◽  
Lyra Manifold ◽  
Expansion Behavior ◽  
Rotationally Symmetric ◽  
Present Universe ◽  
Bianchi Type I Universe ◽  
The Universe

In the course of investigation of our present universe by considering the five-dimensional locally rotationally symmetric (LRS) Bianchi type-I universe with time-dependent deceleration parameters in Lyra manifold, it is excitingly found that the geometry itself of Lyra manifold behaves and consistent with present observational findings for accelerating universe. The behavior of the universes and their contribution to the process of evolution are examined. While studying their physical, dynamical and kinematical properties for different cases, it is found that this model is a new and viable form of model universe containing dark energy. It will be very helpful in explaining the present accelerated expansion behavior of the universe.

scholarly journals Some exact solutions in f(𝒢,T) gravity via Noether symmetries

2017 ◽  
Vol 32 (16) ◽  
pp. 1750086 ◽  
Author(s):  
M. Farasat Shamir ◽  
Mushtaq Ahmad
Keyword(s):  
Exact Solutions ◽  
Momentum Tensor ◽  
Gravity Models ◽  
Noether Symmetry ◽  
Type I ◽  
Conserved Quantities ◽  
Rotationally Symmetric ◽  
Bianchi Type I Universe ◽  
Modified Formula ◽  
Bonnet Term

This paper is devoted to investigate the recently proposed modified Gauss–Bonnet [Formula: see text] gravity, with [Formula: see text], the Gauss–Bonnet term, coupled with [Formula: see text], the trace of energy–momentum tensor. We have used the Noether symmetry methodology to discuss some cosmologically important [Formula: see text] gravity models with anisotropic background. In particular, the Noether symmetry equations for modified [Formula: see text] gravity are reported for locally rotationally symmetric Bianchi type I universe. Explicitly, two models have been proposed to explore the exact solutions and the conserved quantities. It is concluded that the specific models of modified Gauss–Bonnet gravity may be used to reconstruct [Formula: see text]CDM cosmology without involving any cosmological constant.

The Mimetic Matter in LRS Bianchi Type-I Model

2021 ◽  
Author(s):  
Ertan Gudekli ◽  
E. Demir
Keyword(s):  
Bianchi Type ◽  
State Parameter ◽  
Relativity Theory ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Rotationally Symmetric ◽  
Bianchi Type I Universe ◽  
Expansion Of The Universe ◽  
The Universe

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.

scholarly journals IR quantum gravity solves naturally cosmic acceleration and its coincidence problem

2019 ◽  
Vol 28 (14) ◽  
pp. 1944013
Author(s):  
Fotios K. Anagnostopoulos ◽  
Georgios Kofinas ◽  
Vasilios Zarikas
Keyword(s):  
Quantum Gravity ◽  
Cosmic Acceleration ◽  
Fine Tuning ◽  
Accelerated Expansion ◽  
The Novel ◽  
Positive Cosmological Constant ◽  
Coincidence Problem ◽  
Expansion Of The Universe ◽  
Free Parameters ◽  
The Universe

The novel idea is that the undergoing accelerated expansion of the universe happens due to infrared quantum gravity modifications at intermediate astrophysical scales of galaxies or galaxy clusters, within the framework of Asymptotically Safe gravity. The reason is that structures of matter are associated with a scale-dependent positive cosmological constant of quantum origin. In this context, no extra unproven energy scales or fine-tuning are used. Furthermore, this model was confronted with the most recent observational data from a variety of probes, and with the aid of Bayesian analysis, the most probable values of the free parameters were extracted. Finally, the model proved to be statistically equivalent with [Formula: see text]CDM, and thus being able to resolve naturally the concept of dark energy and its associated cosmic coincidence problem.

Interactions in the dark sector within the scope of Bianchi type-V model

2020 ◽  
Vol 35 (27) ◽  
pp. 2050226
Author(s):  
Ruslan K. Muharlyamov ◽  
Tatiana N. Pankratyeva
Keyword(s):  
Bianchi Type ◽  
Accelerated Expansion ◽  
Dark Sector ◽  
Coincidence Problem ◽  
Linear Interaction ◽  
Anisotropic Dark Energy ◽  
Expansion Of The Universe ◽  
Type V ◽  
Parameter Values ◽  
Bianchi Type V

We are building a cosmological model that has small anisotropy and curvature. For this purpose, the Bianchi type-V (BV) model with dark matter (DM) and anisotropic dark energy (DE) is considered. Assuming a law for deviation from the equation of state (Eos) of DE is linear, we study the transition from decelerated to late accelerated expansion of the Universe. In the proposed model, the linear interaction of the two components alleviates the coincidence problem of the present Universe. Examples of model parameter values compatible with observational data are given.

scholarly journals F(T) MODELS WITHIN BIANCHI TYPE-I UNIVERSE

2011 ◽  
Vol 26 (22) ◽  
pp. 1657-1671 ◽  
Author(s):  
M. SHARIF ◽  
SHAMAILA RANI
Keyword(s):  
Equation Of State ◽  
Bianchi Type ◽  
State Parameter ◽  
Conservation Equation ◽  
Cosmic Acceleration ◽  
Type I ◽  
Bianchi Type I ◽  
Constant Solution ◽  
Equation Of State Parameter ◽  
Bianchi Type I Universe

In this paper, we consider spatially homogeneous and anisotropic Bianchi type I universe in the context of F(T) gravity. We construct some corresponding models using conservation equation and equation of state parameter representing different phases of the universe. In particular, we take matter-dominated era, radiation-dominated era, present dark energy phase and their combinations. It is found that one of the models has a constant solution which may correspond to the cosmological constant. We also derive equation of state parameter by using two well-known F(T) models and discuss cosmic acceleration.

scholarly journals Stability of the Universe Model Coupled with Phantom and Tachyon Fields

2019 ◽  
Vol 2019 ◽  
pp. 1-16 ◽  
Author(s):  
M. Sharif ◽  
Saadia Mumtaz
Keyword(s):  
Critical Points ◽  
Bianchi Type ◽  
Dynamical Analysis ◽  
Type I ◽  
Universe Model ◽  
Cosmic Expansion ◽  
Rotationally Symmetric ◽  
Coupled Field ◽  
Bianchi Type I Universe ◽  
The Universe

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.

Locally rotationally symmetric Bianchi type-I string cosmological models in f(R) theory of gravity

2018 ◽  
Vol 15 (09) ◽  
pp. 1850156 ◽  
Author(s):  
Y. Aditya ◽  
D. R. K. Reddy
Keyword(s):  
Bianchi Type ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Cosmic Acceleration ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Locally Rotationally Symmetric ◽  
Rotationally Symmetric ◽  
Theory Of Gravity

This study deals with spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type-I universe with cosmic string source in the framework of [Formula: see text] theory of gravity [S. Capozziello, S. Carloni and A. Troisi, Quintessence without scalar fields, Recent Res. Dev. Astron. Astrophys. 1 (2003), 625; S. Nojiri and S. D. Odintsov, Modified gravity with negative and positive powers of curvature: Unification of inflation and cosmic acceleration, Phys. Rev. D 68 (2003) 123512]. Solving the field equations using (i) relation between metric potentials, (ii) power law relation between [Formula: see text] and average scale factor [Formula: see text] and (iii) equations of state for string models we have presented Takabayasi [T. Takabayasi, Quantum Mechanics Determinism, Causality, and Particles (Springer, Berlin, 1976)], Nambu [P. S. Letelier, String cosmologies, Phys. Rev. D 28 (1983) 2414–2419] and Reddy [D. R. K. Reddy, A string cosmological model in a scalar–Tensor theory of gravitation, Astrophys. Space Sci. 286 (2003) 359–363] string cosmological models. The dynamical parameters of our models are determined and their physical behavior is discussed. The most interesting result about the models is that the anisotropic effects are wiped out at late times.

Locally rotationally symmetric Bianchi type I cosmology in f(R) gravity

2015 ◽  
Vol 93 (1) ◽  
pp. 37-42 ◽  
Author(s):  
M. Farasat Shamir ◽  
Zahid Raza
Keyword(s):  
Bianchi Type ◽  
Type I ◽  
Field Equations ◽  
Three Solutions ◽  
Bianchi Type I ◽  
Locally Rotationally Symmetric ◽  
Expansion Scalar ◽  
Rotationally Symmetric ◽  
Bianchi Type I Universe ◽  
Killing Symmetries

This manuscript is devoted to investigating a Bianchi type I universe in the context of f(R) gravity. For this purpose, we explore the exact solutions of locally rotationally symmetric Bianchi type I space–time in the metric version of f(R) gravity. The modified field equations are solved by assuming the expansion scalar θ to be proportional to the shear scalar σ, which gives A = Bn, where A and B are the metric coefficients, and n is an arbitrary constant. In particular, three solutions have been found and corresponding Killing symmetries are calculated in each case.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

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