scholarly journals Cosmological constant in chameleon Brans–Dicke theory

2019 ◽  
Vol 28 (01) ◽  
pp. 1950022 ◽  
Author(s):  
Yousef Bisabr
Keyword(s):  
Exact Solution ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Exact Solutions ◽  
Effective Mass ◽  
Potential Function ◽  
Power Law ◽  
Exponential Form ◽  
First Case ◽  
Different Types

We consider a generalized Brans–Dicke model in which the scalar field has a self-interacting potential function. The scalar field is also allowed to couple nonminimally with the matter part. We assume that it has a chameleon behavior in the sense that it acquires a density-dependent effective mass. We consider two different types of matter systems which couple with the chameleon, dust and vacuum. In the first case, we find a set of exact solutions when the potential has an exponential form. In the second case, we find a power-law exact solution for the scale factor. In this case, we will show that the vacuum density decays during expansion due to coupling with the chameleon.

scholarly journals SCALAR FIELD COSMOLOGIES WITH VISCOUS FLUID

1996 ◽  
Vol 05 (03) ◽  
pp. 313-318 ◽  
Author(s):  
LUIS P. CHIMENTO ◽  
ALEJANDRO S. JAKUBI
Keyword(s):  
Scalar Field ◽  
Viscous Fluid ◽  
Cosmological Constant ◽  
Exact Solutions ◽  
Power Law ◽  
Asymptotically Stable ◽  
De Sitter ◽  
Nonlinear Viscosity ◽  
Free Scalar ◽  
Linear And Nonlinear

We investigate cosmological models with a free scalar field and a viscous fluid. We find exact solutions for a linear and nonlinear viscosity pressure. Both yield singular and bouncing solutions. In the first regime, a de Sitter stage is asymptotically stable, while in the second case we find power-law evolutions for a vanishing cosmological constant.

scholarly journals Scalar field cosmology in Lyra's geometry

2015 ◽  
Vol 3 (2) ◽  
pp. 117 ◽  
Author(s):  
V. K. Shchigolev ◽  
E. A. Semenova
Keyword(s):  
Exact Solution ◽  
Scalar Field ◽  
Generating Function ◽  
Function Method ◽  
Scalar Fields ◽  
First Order ◽  
Homogeneous Cosmological Models ◽  
Different Types ◽  
Lyra’S Geometry ◽  
Scalar Field Cosmology

<p>The new classes of homogeneous cosmological models for the scalar fields are build in the context of Lyra’s geometry. The different types of exact solution for the model are obtained by applying two procedures, viz the generating function method and the first order formalism.</p>

WORMHOLE SOLUTIONS IN R1×S1×S2 TOPOLOGICAL SPACE

1992 ◽  
Vol 07 (27) ◽  
pp. 2463-2467 ◽  
Author(s):  
SUBENOY CHAKRABORTY
Keyword(s):  
Scalar Field ◽  
Topological Space ◽  
Cosmological Constant ◽  
Symmetric Tensor ◽  
Einstein Equations ◽  
Second Step ◽  
Anisotropic Space ◽  
First Case ◽  
Frw Metric ◽  
Conformal Scalar Field

Wormhole solutions are discussed for two different physical situations in the background of a homogeneous anisotropic space-time. In the first case, the wormholes are solutions of the Euclidean Einstein equations with a cosmological constant and a two-index anti-symmetric tensor for monopole configuration on a space with three-surface of topology S1×S2. In the second step, conformal scalar field is coupled to gravity and wormhole are considered for both λ=0 and λ>0. These results are analogous to the wormhole solutions for FRW metric.

Inflationary cosmology for f(R, ϕ) models with different potentials

2017 ◽  
Vol 95 (11) ◽  
pp. 1074-1085 ◽  
Author(s):  
M. Zubair ◽  
Farzana Kousar
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Energy Density ◽  
Cosmological Constant ◽  
Observational Data ◽  
Power Law ◽  
Early Time ◽  
Inflationary Cosmology ◽  
Effective Equation ◽  
Slow Roll

We examine inflation in [Formula: see text] theory, where a scalar field is coupled to gravity. We have constructed [Formula: see text] models using exponential and power law potentials and study inflation for these models, which can support the early-time acceleration with a useful cosmological constant at high curvature. We have calculated the slow-roll parameters, scalar-to-tensor ratio, and spectral index for these models and analyzed them graphically to check the viability according to recent observational data. We have also presented the evolution of effective equation of state and energy density.

scholarly journals Unrivaled quantum vacuum in the primordial universe

2021 ◽  
Vol 36 (01) ◽  
pp. 2150002
Author(s):  
Davood Momeni
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Effective Mass ◽  
Conformal Symmetry ◽  
Early Time ◽  
Late Time ◽  
Quantization Scheme ◽  
Quantum Vacuum ◽  
Vacuum States ◽  
Dominant Part

In a primordial universe pre- (post-)inflationary era, there could be phases of early universe made of cold gas baryons, radiation and early post-inflationary cosmological constant. I showed that in the baryonic epoch, the quantum vacuum is unique. By using the standard quantization scheme for a massive minimally coupled scalar field with maximal conformal symmetry in the classical space–time, I demonstrated that the scalar modes had an effective mass [Formula: see text] (or [Formula: see text]). This argument was validated when the conformal time [Formula: see text] kept so close to the inflation ending time [Formula: see text]. The energy density of the baryonic matter diverged at the inflation border and vanishes at the late time future. Furthermore, I argued that at very early accelerating epoch when the radiation was the dominant part in the close competition with the early time cosmological constant, fine-tuned mass of the scalar field [Formula: see text] also provided a unique quantum vacuum. The reason is that the effective mass eventually is vanished. A remarkable observation was that all the other possible vacuum states “squeezed” eternally.

scholarly journals EXACT SOLUTIONS OF EMBEDDING THE 4D UNIVERSE IN A 5D EINSTEIN MANIFOLD

2008 ◽  
Vol 17 (02) ◽  
pp. 257-263 ◽  
Author(s):  
XIN-HE MENG ◽  
JIE REN ◽  
HONG-GUANG ZHANG
Keyword(s):  
Cosmological Constant ◽  
Exact Solutions ◽  
Einstein Equation ◽  
Power Law ◽  
Einstein Manifold ◽  
Spatial Dimension ◽  
Λcdm Model ◽  
Extra Spatial Dimension ◽  
The Right ◽  
Real Universe

One of the simplest ways to extend 4D cosmological models is to add another spatial dimension to make them 5D. In particular, it has been shown that the simplest of such 5D models, i.e. one in which the right-hand side of the Einstein equation is empty, induces a 4D nonempty universe. Accordingly, the origin of matter in a real 4D universe might be mathematically attributed to the existence of one (fictitious) extra spatial dimension. Here we consider the case of an empty 5D universe possessing a cosmological constant Λ and obtain exact solutions for both positive and negative values of the Λ. It is seen that such a model can naturally reduce to a power law ΛCDM model for the real universe. Further, it can be seen that the arbitrary constants and functions appearing in this model are endowed with definite physical meanings.

scholarly journals COSMOLOGICAL CONSTANT, GENERATION OF DIMENSIONS AND THE EFFECTS OF ANISOTROPY IN MULTIDIMENSIONAL SPACETIME

2012 ◽  
Vol 27 (15) ◽  
pp. 1250088
Author(s):  
SERGEY V. YAKOVLEV
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Effective Mass ◽  
Vacuum Energy ◽  
Initial Conditions ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Dimensional Spacetime ◽  
Higher Dimensional

In the paper, multidimensional anisotropic metric and density of vacuum energy in the Kasner's model are investigated. It is shown that the presence of scalar field in model is equivalent to metric in the spacetime with additional dimensions and we propose the idea of generating additional dimensions by massless scalar field. We propose a method of renormalization of metric that describes conversion from spacetime with scalar field to higher-dimensional spacetime. We obtain the expression for cosmological constant which depends on the initial conditions for anisotropic metric coefficients. Using the method of Bogolubov, we investigate the influence of anisotropic metric onto the cosmological birth of particles and obtain the effective mass of scalar field depending on the cosmological constant.

scholarly journals COSMOLOGICAL MODEL OF INTERACTING TACHYON FIELD

2012 ◽  
Vol 27 (17) ◽  
pp. 1250086 ◽  
Author(s):  
V. K. SHCHIGOLEV ◽  
M. P. ROTOVA
Keyword(s):  
Exact Solution ◽  
Scalar Field ◽  
Cosmological Model ◽  
Energy Flow ◽  
Field Model ◽  
Scalar Fields ◽  
Tachyon Field ◽  
First Order ◽  
Different Types ◽  
Phantom Fields

In this paper we investigate a tachyon field model in cosmology, provided its interaction with the quintessence or phantom fields. The model takes into account this interaction beyond the usual approach, in which the interaction is phenomenologically described by the energy flow between the matter components. In our model, the interaction of tachyon field with a canonical scalar field is taken into account through the interaction potential in the total Lagrangian of the system, like in the case of two or more canonical scalar fields. We obtain the different types of exact solution for the model by employing the so-called "first order formalism" procedures.

scholarly journals EXACT SOLUTION FOR THE MASSLESS CYLINDRICALLY SYMMETRIC SCALAR FIELD IN GENERAL RELATIVITY, WITH COSMOLOGICAL CONSTANT

2009 ◽  
Vol 24 (31) ◽  
pp. 5991-6000 ◽  
Author(s):  
D. MOMENI ◽  
H. MIRAGHAEI
Keyword(s):  
Exact Solution ◽  
General Relativity ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Cylindrical Symmetry ◽  
Cosmological Models ◽  
Cyclic Universe ◽  
Cylindrically Symmetric

In this paper, we present a new exact solution for scalar field with cosmological constant in cylindrical symmetry. Associated cosmological models, including a model that describes a cyclic universe, are discussed.

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