scholarly journals A Quintessence Problem in Self-Interacting Brans–Dicke Theory

2003 ◽  
Vol 18 (19) ◽  
pp. 3315-3323 ◽  
Author(s):  
Subenoy Chakraborty ◽  
Narayan Chandra Chakraborty ◽  
Ujjal Debnath
Keyword(s):  
Scalar Field ◽  
Present Universe ◽  
Flatness Problem

A quintessence scalar field in self-interacting Brans–Dicke theory is shown to give rise to a nondecelerated expansion of the present universe for open, flat and closed models. Along with providing a nondecelerating solution, it can potentially solve the flatness problem too.

scholarly journals BRANS–DICKE COSMOLOGY IN AN ANISOTROPIC MODEL WHEN VELOCITY OF LIGHT VARIES

2002 ◽  
Vol 11 (06) ◽  
pp. 921-932 ◽  
Author(s):  
SUBENOY CHAKRABORTY ◽  
NARAYAN CHANDRA CHAKRABORTY ◽  
UJJAL DEBNATH
Keyword(s):  
Scalar Field ◽  
Asymptotic Behaviour ◽  
Space Time ◽  
Anisotropic Model ◽  
Time Model ◽  
Velocity Of Light ◽  
Space Time Model ◽  
Flatness Problem

In this paper, we have studied Brans–Dicke (BD) Cosmology in an anisotropic Kantowski–Sachs space–time model; considering variation of the velocity of light. We have addressed the flatness problem considering both cases namely (i) when the Brans–Dicke scalar field φ is constant (ii) when φ varies, specially for radiation dominated era perturbatively and non-perturbatively and asymptotic behaviour have been studied.

scholarly journals A QUINTESSENCE PROBLEM IN BRANS–DICKE THEORY WITH VARYING SPEED OF LIGHT

2003 ◽  
Vol 12 (02) ◽  
pp. 325-335 ◽  
Author(s):  
SUBENOY CHAKRABORTY ◽  
NARAYAN CHANDRA CHAKRABORTY ◽  
UJJAL DEBNATH
Keyword(s):  
Scalar Field ◽  
Speed Of Light ◽  
Anisotropic Models ◽  
Present Universe

It is shown that minimally coupled scalar field in Brans–Dicke theory with varying speed of light can solve the quintessence problem and it is possible to have a non-decelerated expansion of the present universe with Brans–Dicke-theory for anisotropic models without any matter.

scholarly journals Model of a multiverse providing the dark energy of our universe

2017 ◽  
Vol 32 (25) ◽  
pp. 1750149 ◽  
Author(s):  
E. Rebhan
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Mass Density ◽  
Spatial Curvature ◽  
Dark Energy Density ◽  
A Value ◽  
Local Fluctuations ◽  
Parallel Universes ◽  
Flatness Problem ◽  
Standard Concept

It is shown that the dark energy presently observed in our universe can be regarded as the energy of a scalar field driving an inflation-like expansion of a multiverse with ours being a subuniverse among other parallel universes. A simple model of this multiverse is elaborated: Assuming closed space geometry, the origin of the multiverse can be explained by quantum tunneling from nothing; subuniverses are supposed to emerge from local fluctuations of separate inflation fields. The standard concept of tunneling from nothing is extended to the effect that in addition to an inflationary scalar field, matter is also generated, and that the tunneling leads to an (unstable) equilibrium state. The cosmological principle is assumed to pertain from the origin of the multiverse until the first subuniverses emerge. With increasing age of the multiverse, its spatial curvature decays exponentially so fast that, due to sharing the same space, the flatness problem of our universe resolves by itself. The dark energy density imprinted by the multiverse on our universe is time-dependent, but such that the ratio [Formula: see text] of its mass density and pressure (times [Formula: see text]) is time-independent and assumes a value [Formula: see text] with arbitrary [Formula: see text]. [Formula: see text] can be chosen so small, that the dark energy model of this paper can be fitted to the current observational data as well as the cosmological constant model.

Theoretical constraints on kinetic k-essence dark energy model in El-Nabulsi fractional action cosmology

2013 ◽  
Vol 91 (10) ◽  
pp. 844-849 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Scalar Field ◽  
Dark Energy Model ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Phantom Divide ◽  
Fractional Action Cosmology ◽  
Present Universe ◽  
Phantom Divide Line ◽  
The Universe

In this work, we considered an effective scalar field theory described by a Lagrangian with a noncanonical kinetic term, which leads to accelerated expansion in the present Universe and is known as k-essence in the framework of the fractional action cosmology recently introduced by El-Nabulsi. We have chosen a particular ansatz for the scale factor and the scalar field, in which both are described as a power-law of the time, t. We have studied the behavior of some cosmological quantities in other models to obtain some useful information about the model considered. We observed that the equation of state parameter, w, has decreasing behavior and it never crosses the phantom divide line (i.e., w = –1). Studying the statefinder pair {r, s} and {w, w′}, we observed that the model considered is able to obtain the ΛCDM phase of the Universe.

scholarly journals Dark Matter and Dark Energy in the Universe

BIBECHANA ◽  
2014 ◽  
Vol 11 ◽  
pp. 8-16 ◽  
Author(s):  
BC Paul
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Particle Physics ◽  
Late Phase ◽  
Exponential Phase ◽  
Astronomical Observations ◽  
The Standard Model ◽  
Present Universe ◽  
The Universe

Cosmological and astronomical observations predict that the present Universe is passing through an accelerating phase of expansion. The Universe emerged out of an exponential phase in the very early Universe. The scalar field of the standard model of particle physics when used in cosmology admits such a phase of expansion known as inflation. The most favourable condition for inflation with scalar field to admit an Inflationary scenario is that the potential energy must dominate over the kinetic energy which one obtains with a flat potential. Thereafter the Universe enters into a matter dominated phase when the field oscillates at the minimum of the potential. But it is not possible to accommodate the present accelerating phase in the Einstein’s gravity. It is known from observational analysis that about 73 % matter is responsible for the late phase expansion and 23 % matter called Dark Matter is responsible for a stable galaxy. We discuss here the relevant fields and theories that are useful for describing the late Universe. DOI: http://dx.doi.org/10.3126/bibechana.v11i0.10374 BIBECHANA 11(1) (2014) 8-16

scholarly journals Numerical analysis of spin foam dynamics and the flatness problem

2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Pietro Donà ◽  
Francesco Gozzini ◽  
Giorgio Sarno
Keyword(s):  
Numerical Analysis ◽  
Spin Foam ◽  
Flatness Problem
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