scholarly journals Toy Models of Universe with an Effective VaryingΛ-Term in Lyra Manifold

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Martiros Khurshudyan
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Accelerated Expansion ◽  
Observational Constraints ◽  
Constant Deceleration Parameter ◽  
Expansion Phase ◽  
Lyra Manifold ◽  
New Form ◽  
Transit Universe ◽  
The Universe

Research on the accelerated expansion of our Universe captures a lot of attention. The dark energy (DE) is a way to explain it. In this paper we will consider scalar field quintessence DE withωDE>-1EoS, where the dynamics of the DE models related to the dynamics of the scalar field. We are interested in the study of the behavior of the Universe in the presence of interacting quintessence DE models in Lyra manifold with a varyingΛt. In a considered framework we also would like to propose a new form forΛt. We found that the models correspond to the transit Universe, which will enter the accelerated expansion phase and will remain there with a constant deceleration parameterq. We found also that theΛtis a decreasing function which takes a small positive value withΩm≠0andΩQ→constdominatingΩmin the old Universe. Observational constraints are applied and causality issue viaCS2is discussed as a possible way to either reject or accept the models.

scholarly journals A novel teleparallel dark energy model

2016 ◽  
Vol 25 (02) ◽  
pp. 1650025 ◽  
Author(s):  
Giovanni Otalora
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Teleparallel Gravity ◽  
Accelerated Expansion ◽  
Late Time ◽  
De Sitter ◽  
Sitter Group ◽  
Current State ◽  
Expansion Of The Universe ◽  
The Universe

Although equivalent to general relativity, teleparallel gravity (TG) is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the “vector torsion”. This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group [Formula: see text]. It is found that the current state of accelerated expansion of the universe corresponds to a late-time attractor that can be (i) a dark energy-dominated de Sitter solution ([Formula: see text]), (ii) a quintessence-type solution with [Formula: see text], or (iii) a phantom-type [Formula: see text] dark energy.

Kaluza–Klein minimally interacting dark energy model in the presence of massive scalar field

2021 ◽  
Vol 36 (08) ◽  
pp. 2150054
Author(s):  
K. Dasu Naidu ◽  
Y. Aditya ◽  
R. L. Naidu ◽  
D. R. K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Eos Parameter ◽  
Massive Scalar Field ◽  
The Universe ◽  
Kaluza Klein

In this paper, our purpose is to discuss the dynamical aspects of Kaluza–Klein five-dimensional cosmological model filled with minimally interacting baryonic matter and dark energy (DE) in the presence of an attractive massive scalar field. We obtain a determinate solution of the Einstein field equations using (i) a relation between the metric potentials and (ii) a power law relation between the average scale factor of the universe and the massive scalar field. We have determined scalar field, matter energy density, DE density, equation of state (EoS) [Formula: see text], deceleration [Formula: see text] and statefinder [Formula: see text] parameters of our model. We also develop [Formula: see text]–[Formula: see text] phase, squared sound speed, statefinders and [Formula: see text]–[Formula: see text] planes in the evolving universe. It is observed that the EoS parameter exhibits quintom-like behavior from quintessence to phantom epoch by crossing the vacuum era of the universe. The squared speed of sound represents the instability of the model, whereas the [Formula: see text]–[Formula: see text] plane shows both thawing and freezing regions. The [Formula: see text]CDM limit is attained in both [Formula: see text]–[Formula: see text] and statefinder planes. We have also discussed the cosmological importance of the above parameters with reference to modern cosmology. It is found that the dynamics of these cosmological parameters indicate the accelerated expansion of the universe which is consistent with the current cosmological observations.

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 COSMIC ACCELERATION IN A MODEL OF SCALAR–TENSOR GRAVITATION

2008 ◽  
Vol 17 (11) ◽  
pp. 2007-2015 ◽  
Author(s):  
SANIL UNNIKRISHNAN ◽  
T. R. SESHADRI
Keyword(s):  
Scalar Field ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Observational Constraints ◽  
Gravitational Coupling ◽  
Effective Equation ◽  
Expansion Phase ◽  
Tensor Theory ◽  
Theory Of Gravitation ◽  
Cosmological Consequence

In this paper we consider a model of the scalar–tensor theory of gravitation, in which the scalar field ϕ determines the gravitational coupling G and has a Lagrangian of the form [Formula: see text]. We study the cosmological consequence of this theory in the matter-dominated era and show that it leads to a transition from an initial decelerated expansion to an accelerated expansion phase at the present epoch. Using observational constraints, we see that the effective equation of state today for the scalar field turns out to be pϕ = wϕρϕ, with wϕ = -0.88, and that the transition to an accelerated phase happened at a redshift of about 0.3.

Tsallis holographic dark energy models in axially symmetric space time

2020 ◽  
Vol 17 (01) ◽  
pp. 2050011 ◽  
Author(s):  
Vipin Chandra Dubey ◽  
Ambuj Kumar Mishra ◽  
Shikha Srivastava ◽  
Umesh Kumar Sharma
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Holographic Dark Energy ◽  
Field Potential ◽  
Accelerated Expansion ◽  
Anisotropic Universe ◽  
Axially Symmetric ◽  
Eos Parameter ◽  
Quintessence Field ◽  
The Universe

In this work, we have examined the behavior of Bianchi-I (axially symmetric) matter-dominated and the anisotropic Universe with the proposed dark energy, Tsallis holographic dark energy (THDE), with the Hubble horizon as infrared cut-off [Tavayef et al., Tsallis holographic dark energy, Phys. Lett. B 781 (2018) 195–200]. The Universe evolution from matter-dominated epoch to dark energy dominated epoch is described by our proposed THDE model. The EoS parameter in our THDE model explains the evolution of the Universe according to the value of nonextensive or Tsallis parameter [Formula: see text], phantom era ([Formula: see text]) or quintom (phantom line crossing) and the quintessence era ([Formula: see text]), before reaching to completely dark energy-dominated era in the future. Additionally, we also plan to reconcile the dark energy by the method of reconstructing the evolution of the scalar field potential. For the analysis, we take into account the quintessence field and phantom scalar field for this reconstruction, which at present shows the accelerated expansion.

Kantowski–Sachs universe with dark energy fluid and massive scalar field

2020 ◽  
Vol 98 (11) ◽  
pp. 993-998
Author(s):  
K. Deniel Raju ◽  
M.P.V.V. Bhaskara Rao ◽  
Y. Aditya ◽  
T. Vinutha ◽  
D.R.K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Massive Scalar Field ◽  
Anisotropic Dark Energy ◽  
Expansion Of The Universe ◽  
The Universe

This study is mainly concerned with a spatially homogeneous and anisotropic Kantowski–Sachs cosmological model with anisotropic dark energy fluid and massive scalar field. We solve the field equations using (i) the shear scalar proportionality to the expansion scalar and (ii) a mathematical condition that is a consequence of the power law between the scalar field and the average scale factor of the universe, and the corresponding dark energy model is presented. The cosmological parameters of the model are computed and discussed, as well as the relevance of its dynamical aspects to the recent scenario of the accelerated expansion of the universe.

scholarly journals Reconstructing the evolution of dark energy with variations of fundamental parameters

2009 ◽  
Vol 5 (H15) ◽  
pp. 303-303
Author(s):  
N. J. Nunes ◽  
T. Dent ◽  
C. J. A. P. Martins ◽  
G. Robbers
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Structure Constant ◽  
Dynamical Evolution ◽  
Accelerated Expansion ◽  
Fine Structure Constant ◽  
Quasar Absorption Lines ◽  
Fundamental Parameters ◽  
Expansion Of The Universe ◽  
The Universe

A popular candidate of dark energy, currently driving an accelerated expansion of the universe, is a slowly rolling scalar field or quintessence. A scalar field, however, must couple with other sources of matter. Consequently, its dynamical evolution can result in extra interactions between standard particles, which are mediated by the field, and to a variation in the fundamental parameters. Curiously, it has been reported that observations of a number of quasar absorption lines suggest that the fine structure constant was smaller in the past, at redshifts in the range z=1-3 (Murphy et al. (2003), Murphy et al. (2004), but see also Srianand et al. (2007)). Could this indeed be the signature of a slowly evolving scalar field?

scholarly journals Ghost Chaplygin scalar field model of dark energy

2013 ◽  
Vol 91 (1) ◽  
pp. 54-59 ◽  
Author(s):  
F. Adabi ◽  
K. Karami ◽  
M. Mousivand
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Field Model ◽  
Accelerated Expansion ◽  
Scalar Field Model ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

We investigate the correspondence between the ghost and Chaplygin scalar field dark energy models in the framework of Einstein gravity. We consider a spatially nonflat Friedmann–Robertson–Walker universe containing dark energy that interacts with dark matter. We reconstruct the potential and the dynamics for the Chaplygin scalar field model according to the evolutionary behavior of ghost dark energy, which can describe the phantomic accelerated expansion of the universe.

Inflation and dark energy in f(R, X, ϕ) gravity

2018 ◽  
Vol 33 (36) ◽  
pp. 1850215 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Observational Data ◽  
Observational Constraints ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we show the early inflation and the late-time acceleration of the universe in the model [Formula: see text], which shows a minimum connection between geometry and scalar field. Both a quintessential inflation and the super inflation mechanism are discussed in the model, and for both the cases the some conditions for n are obtained under the constraint of the observational data. However, the oscillations of the scalar field are analyzed in view of observational constraints. By means of the oscillations of the scalar field, besides the inflation of the universe a condition of n for the late-time quintessence type of dark energy is obtained.

Cosmological implications of scalar field dark energy models in f(T,𝒯 ) gravity

2018 ◽  
Vol 15 (04) ◽  
pp. 1850063 ◽  
Author(s):  
Ines G. Salako ◽  
Abdul Jawad ◽  
Hooman Moradpour
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Scalar Potential ◽  
Momentum Tensor ◽  
Accelerated Expansion ◽  
Frw Universe ◽  
Equation Of States ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
The Universe

After reviewing the [Formula: see text] gravity, in which [Formula: see text] is the torsion scalar and [Formula: see text] is the trace of the energy-momentum tensor, we refer to two cosmological models of this theory in agreement with observational data. Thereinafter, we consider a flat Friedmann–Robertson–Walker (FRW) universe filled by a pressureless source and look at the terms other than the Einstein terms in the corresponding Friedmann equations, as the dark energy (DE) candidate. In addition, some cosmological features of models, including equation of states and deceleration parameters, are addressed helping us in getting the accelerated expansion of the universe in quintessence era. Finally, we extract the scalar field as well as potential of quintessence, tachyon, K-essence and dilatonic fields for both [Formula: see text] models. It is observed that the dynamics of scalar field as well as the scalar potential of these models indicate an accelerated expanding universe in these models.

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