Conformally coupled scalar field solutions and the cosmological constant

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.

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SAVING THE MECHANISM OF A DECAYING COSMOLOGICAL CONSTANT

Modern Physics Letters A ◽

10.1142/s0217732389000629 ◽

1989 ◽

Vol 04 (06) ◽

pp. 513-518 ◽

Cited By ~ 3

Author(s):

YASUNORI FUJII

Keyword(s):

Scalar Field ◽

Simple Model ◽

Cosmological Constant ◽

Gravitational Constant ◽

Atomic Clock ◽

Fifth Force

The mechanism of a decaying cosmological constant in terms of a scalar field has been criticized for its ensuing diminishment of the gravitational constant with time. Contrary to a naive view, however, the physical results can be made fully nontrivial, as demonstrated explicitly by a simple model in which the scalar field generates particle masses that increase with time, but in such a way that the gravitational constant stays constant asymptotically when time is measured by an atomic clock. The scalar field might also be an origin of the fifth force.

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The Effect of a Positive Cosmological Constant on the Bounce of Loop Quantum Cosmology

Mathematics ◽

10.3390/math8020186 ◽

2020 ◽

Vol 8 (2) ◽

pp. 186

Author(s):

Mercedes Martín-Benito ◽

Rita B. Neves

Keyword(s):

Scalar Field ◽

Cosmological Constant ◽

Quantum Cosmology ◽

Quantum Dynamics ◽

Solvable Model ◽

Massless Scalar ◽

Loop Quantum Cosmology ◽

Massless Scalar Field ◽

Positive Cosmological Constant ◽

Semiclassical States

We provide an analytical solution to the quantum dynamics of a flat Friedmann-Lemaître- Robertson-Walker model with a massless scalar field in the presence of a small and positive cosmological constant, in the context of Loop Quantum Cosmology. We use a perturbative treatment with respect to the model without a cosmological constant, which is exactly solvable. Our solution is approximate, but it is precisely valid at the high curvature regime where quantum gravity corrections are important. We compute explicitly the evolution of the expectation value of the volume. For semiclassical states characterized by a Gaussian spectral profile, the introduction of a positive cosmological constant displaces the bounce of the solvable model to lower volumes and to higher values of the scalar field. These displacements are state dependent, and in particular, they depend on the peak of the Gaussian profile, which measures the momentum of the scalar field. Moreover, for those semiclassical states, the bounce remains symmetric, as in the vanishing cosmological constant case. However, we show that the behavior of the volume is more intricate for generic states, leading in general to a non-symmetric bounce.

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Quantum of the bare cosmological constant

Progress of Theoretical and Experimental Physics ◽

10.1093/ptep/ptaa039 ◽

2020 ◽

Vol 2020 (4) ◽

Author(s):

Farhang Loran

Keyword(s):

Scalar Field ◽

Cosmological Constant ◽

Stress Tensor ◽

Parameter Space ◽

Field Theories ◽

Classical Solutions ◽

Curved Spacetimes ◽

Free Scalar ◽

Scalar Theories

Abstract We show that there exist scalar field theories with plausible one-particle states in general $D$-dimensional nonstationary curved spacetimes whose propagating modes are localized on $d\le D$ dimensional hypersurfaces, and the corresponding stress tensor resembles the bare cosmological constant $\lambda_{\rm B}$ in the $D$-dimensional bulk. We show that nontrivial $d=1$ dimensional solutions correspond to $\lambda_{\rm B}< 0$. Considering free scalar theories, we find that for $d=2$ the symmetry of the parameter space of classical solutions corresponding to $\lambda_{\rm B}\neq 0$ is $O(1,1)$, which enhances to $\mathbb{Z}_2\times{\rm Diff}(\mathbb{R}^1)$ at $\lambda_{\rm B}=0$. For $d>2$ we obtain $O(d-1,1)$, $O(d-1)\times {\rm Diff}(\mathbb{R}^1)$, and $O(d-1,1)\times O(d-2)\times {\rm Diff}(\mathbb{R}^1)$ corresponding to, respectively, $\lambda_{\rm B}<0$, $\lambda_{\rm B}=0$, and $\lambda_{\rm B}>0$.

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WORMHOLE SOLUTIONS IN R1×S1×S2 TOPOLOGICAL SPACE

Modern Physics Letters A ◽

10.1142/s0217732392003918 ◽

1992 ◽

Vol 07 (27) ◽

pp. 2463-2467 ◽

Cited By ~ 1

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.

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Dark Energy as a Cosmological Consequence of Existence of the Dirac Scalar Field in Nature

Physics Research International ◽

10.1155/2015/952181 ◽

2015 ◽

Vol 2015 ◽

pp. 1-6 ◽

Cited By ~ 3

Author(s):

O. V. Babourova ◽

B. N. Frolov

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Cosmological Constant ◽

Early Universe ◽

Large Time ◽

Field Equations ◽

Conformal Theory ◽

Effective Cosmological Constant ◽

Theory Of Gravitation ◽

Cosmological Consequence

The solution of the field equations of the conformal theory of gravitation with Dirac scalar field in Cartan-Weyl spacetime at the very early Universe is obtained. In this theory dark energy (described by an effective cosmological constant) is a function of the Dirac scalar field β. This solution describes the exponential decreasing of β at the inflation stage and has a limit to a constant value of the dark energy at large time. This can give a way to solving the fundamental cosmological constant problem as a consequence of the fields dynamics in the early Universe.

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Vacuum Expectation Value Profiles of the Bulk Scalar Field in the Generalized Randall-Sundrum Model

Advances in High Energy Physics ◽

10.1155/2015/590980 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10

Author(s):

A. Tofighi ◽

M. Moazzen ◽

A. Farokhtabar

Keyword(s):

Scalar Field ◽

Boundary Conditions ◽

Cosmological Constant ◽

Vacuum Expectation ◽

Vacuum Expectation Value ◽

Brane World ◽

Dirichlet Boundary Conditions ◽

World Model ◽

Expectation Value ◽

Bulk Scalar Field

In the generalized Randall-Sundrum warped brane-world model the cosmological constant induced on the visible brane can be positive or negative. In this paper we investigate profiles of vacuum expectation value of the bulk scalar field under general Dirichlet and Neumann boundary conditions in the generalized warped brane-world model. We show that the VEV profiles generally depend on the value of the brane cosmological constant. We find that the VEV profiles of the bulk scalar field for a visible brane with negative cosmological constant and positive tension are quite distinct from those of Randall-Sundrum model. In addition we show that the VEV profiles for a visible brane with large positive cosmological constant are also different from those of the Randall-Sundrum model. We also verify that Goldberger and Wise mechanism can work under nonzero Dirichlet boundary conditions in the generalized Randall-Sundrum model.

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