scholarly journals DISCRETE GRAVITY AND ITS CONTINUUM LIMIT

2005 ◽  
Vol 20 (03) ◽  
pp. 213-225
Author(s):  
YI LING
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Continuum Limit ◽  
Constant Term ◽  
Chaplygin Gas ◽  
Fine Tuning ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Cosmological Singularity ◽  
The Continuum

Recently Gambini and Pullin proposed a new consistent discrete approach to quantum gravity and applied it to cosmological models. One remarkable result of this approach is that the cosmological singularity can be avoided in a general fashion. However, whether the continuum limit of such discretized theories exists is model dependent. In the case of massless scalar field coupled to gravity with Λ=0, the continuum limit can only be achieved by fine tuning the recurrence constant. We regard this failure as the implication that cosmological constant should vary with time. For this reason we replace the massless scalar field by Chaplygin gas which may contribute an effective cosmological constant term with the evolution of the universe. It turns out that the continuum limit can indeed be reached in this case.

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

Mathematics ◽  
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.

scholarly journals SIGNATURE CHANGE BY GUP

2013 ◽  
Vol 22 (05) ◽  
pp. 1350026 ◽  
Author(s):  
T. GHANEH ◽  
F. DARABI ◽  
H. MOTAVALLI
Keyword(s):  
Phase Space ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Generalized Uncertainty Principle ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Massive Scalar ◽  
Good Correspondence ◽  
Massive Scalar Field ◽  
Frw Metric

We revisit the issue of continuous signature transition from Euclidean to Lorentzian metrics in a cosmological model described by Friedmann–Robertson–Walker (FRW) metric minimally coupled with a self-interacting massive scalar field. Then, using a noncommutative (NC) phase space of dynamical variables deformed by generalized uncertainty principle (GUP), we show that the signature transition occurs even for a model described by the FRW metric minimally coupled with a free massless scalar field accompanied by a cosmological constant. This indicates that the continuous signature transition might have been easily occurred at early universe just by a free massless scalar field, a cosmological constant and a NC phase space deformed by GUP, without resorting to a massive scalar field having an ad hoc complicate potential. We also study the quantum cosmology of the model and obtain a solution of Wheeler–DeWitt (WD) equation which shows a good correspondence with the classical path.

scholarly journals GRAVITATIONAL COLLAPSE OF MASSLESS SCALAR FIELD WITH NEGATIVE COSMOLOGICAL CONSTANT IN (2+1) DIMENSIONS

2006 ◽  
Vol 15 (04) ◽  
pp. 545-557 ◽  
Author(s):  
R. CHAN ◽  
M. F. A. DA SILVA ◽  
JAIME F. VILLAS DA ROCHA
Keyword(s):  
Black Holes ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Gravitational Collapse ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Field Equations ◽  
Negative Cosmological Constant ◽  
Global Properties ◽  
Scalar Field Equations

The (2+1)-dimensional geodesic circularly symmetric solutions of Einstein-massless-scalar field equations with negative cosmological constant are found and their local and global properties are studied. It is found that one of them represents gravitational collapse where black holes are always formed.

scholarly journals TURBULENT INSTABILITY OF ANTI-DE SITTER SPACE–TIME

2013 ◽  
Vol 28 (22n23) ◽  
pp. 1340020 ◽  
Author(s):  
MACIEJ MALIBORSKI ◽  
ANDRZEJ ROSTWOROWSKI
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Numerical Study ◽  
De Sitter Space ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Field System ◽  
Technical Details

In these lecture notes, we discuss recently conjectured instability of anti-de Sitter space, resulting in gravitational collapse of a large class of arbitrarily small initial perturbations. We uncover the technical details used in the numerical study of spherically symmetric Einstein-massless scalar field system with negative cosmological constant that led to the conjectured instability.

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 Generating Einstein gravity, cosmological constant and Higgs mass from restricted Weyl invariance

2015 ◽  
Vol 30 (30) ◽  
pp. 1550152 ◽  
Author(s):  
Ariel Edery ◽  
Yu Nakayama
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Higgs Mass ◽  
Higgs Field ◽  
Higgs Sector ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Invariant Action ◽  
Weyl Invariance ◽  
The Standard Model

Recently, it has been pointed out that dimensionless actions in four-dimensional curved spacetime possess a symmetry which goes beyond scale invariance but is smaller than full Weyl invariance. This symmetry was dubbed restricted Weyl invariance. We show that starting with a restricted Weyl invariant action that includes a Higgs sector with no explicit mass, one can generate the Einstein–Hilbert action with cosmological constant and a Higgs mass. The model also contains an extra massless scalar field which couples to the Higgs field (and gravity). If the coupling of this extra scalar field to the Higgs field is negligibly small, this fixes the coefficient of the nonminimal coupling [Formula: see text] between the Higgs field and gravity. Besides the Higgs sector, all the other fields of the Standard Model can be incorporated into the original restricted Weyl invariant action.

scholarly journals Cosmological reconstruction of f(T, 𝒯) gravity

2014 ◽  
Vol 11 (08) ◽  
pp. 1450077 ◽  
Author(s):  
Davood Momeni ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Fluids ◽  
Consistent Model ◽  
The Universe

Motivated by the newly proposal for gravity as the effect of the torsion scalar T and trace of the energy momentum tensor 𝒯, we investigate the cosmological reconstruction of different models of the Universe. Our aim here is to show that how this modified gravity model, f(T, 𝒯) is able to reproduce different epochs of the cosmological history. We explicitly show that f(T, 𝒯) can be reconstructed for ΛCDM as the most popular and consistent model. Also we study the mathematical reconstruction of f(T, 𝒯) for a flat cosmological background filled by two fluids mixture. Such model describes phantom–non-phantom era as well as the purely phantom cosmology. We extend our investigation to more cosmological models like perfect fluid, Chaplygin gas and massless scalar field. In each case we obtain some specific forms of f(T, 𝒯). These families of f(T, 𝒯) contain arbitrary function of torsion and trace of the energy momentum.

scholarly journals Regular black holes in de Sitter universe: Scalar field perturbations and quasinormal modes

2015 ◽  
Vol 24 (14) ◽  
pp. 1550104 ◽  
Author(s):  
Sharmanthie Fernando
Keyword(s):  
Black Hole ◽  
Scalar Field ◽  
Cosmological Constant ◽  
Quasinormal Modes ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
De Sitter ◽  
Regular Black Hole ◽  
Text Mode ◽  
De Sitter Universe

The purpose of this paper is to study quasinormal modes (QNMs) of a regular black hole with a cosmological constant due to scalar perturbations. A detailed study of QNMs frequencies for the massless scalar field was done by varying the parameters of the theory such as mass, magnetic charge, cosmological constant and the spherical harmonic index. We have employed the sixth-order WKB approximation to compute the QNMs frequencies. We have also proved analytically that the [Formula: see text] mode for the massless field reaches a constant value at late times. We have approximated the near-extreme regular-de Sitter (dS) black hole potential with the Pöschl–Teller potential to obtain exact frequencies. The null geodesics of the regular-de Sitter black hole is employed to describe the QNMs frequencies at the eikonal limit ([Formula: see text]).

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