567 research outputs found
Observable Effects of Scalar Fields and Varying Constants
We show by using the method of matched asymptotic expansions that a
sufficient condition can be derived which determines when a local experiment
will detect the cosmological variation of a scalar field which is driving the
spacetime variation of a supposed constant of Nature. We extend our earlier
analyses of this problem by including the possibility that the local region is
undergoing collapse inside a virialised structure, like a galaxy or galaxy
cluster. We show by direct calculation that the sufficient condition is met to
high precision in our own local region and we can therefore legitimately use
local observations to place constraints upon the variation of "constants" of
Nature on cosmological scales.Comment: Invited Festscrift Articl
Dynamical System Approach to Cosmological Models with a Varying Speed of Light
Methods of dynamical systems have been used to study homogeneous and
isotropic cosmological models with a varying speed of light (VSL). We propose
two methods of reduction of dynamics to the form of planar Hamiltonian
dynamical systems for models with a time dependent equation of state. The
solutions are analyzed on two-dimensional phase space in the variables where is a function of a scale factor . Then we show how the
horizon problem may be solved on some evolutional paths. It is shown that the
models with negative curvature overcome the horizon and flatness problems. The
presented method of reduction can be adopted to the analysis of dynamics of the
universe with the general form of the equation of state .
This is demonstrated using as an example the dynamics of VSL models filled with
a non-interacting fluid. We demonstrate a new type of evolution near the
initial singularity caused by a varying speed of light. The singularity-free
oscillating universes are also admitted for positive cosmological constant. We
consider a quantum VSL FRW closed model with radiation and show that the
highest tunnelling rate occurs for a constant velocity of light if and . It is also proved that the considered class of
models is structurally unstable for the case of .Comment: 18 pages, 5 figures, RevTeX4; final version to appear in PR
A time-space varying speed of light and the Hubble Law in static Universe
We consider a hypothetical possibility of the variability of light velocity
with time and position in space which is derived from two natural postulates.
For the consistent consideration of such variability we generalize
translational transformations of the Theory of Relativity. The formulae of
transformations between two rest observers within one inertial system are
obtained. It is shown that equality of velocities of two particles is as
relative a statement as simultaneity of two events is. We obtain the expression
for the redshift of radiation of a rest source which formally reproduces the
Hubble Law. Possible experimental implications of the theory are discussed.Comment: 7 page
Variable Modified Chaplygin Gas and Accelerating Universe
In this letter, I have proposed a model of variable modified Chaplygin gas
and shown its role in accelerating phase of the universe. I have shown that the
equation of state of this model is valid from the radiation era to quiessence
model. The graphical representations of statefinder parameters characterize
different phase of evolution of the universe. All results presented in the
letter concerns the case .Comment: 7 Latex pages, 5 figures, revtex styl
Scaling Solutions and reconstruction of Scalar Field Potentials
Starting from the hypothesis of scaling solutions, the general exact form of
the scalar field potential is found. In the case of two fluids, it turns out to
be a negative power of hyperbolic sine. In the case of three fluids the
analytic form is not found, but is obtained by quadratures.Comment: 5 pages, 2 figures, some changes in references and figures caption
Regularizing cosmological singularities by varying physical constants
Varying physical constant cosmologies were claimed to solve standard
cosmological problems such as the horizon, the flatness and the
-problem. In this paper, we suggest yet another possible application
of these theories: solving the singularity problem. By specifying some examples
we show that various cosmological singularities may be regularized provided the
physical constants evolve in time in an appropriate way.Comment: 9 pages, 6 figures, Revtex4-1, an improved version to appear in JCA
Dynamics of Logamediate and Intermediate Scenarios in the Dark Energy Filled Universe
We have considered a model of two component mixture i.e., mixture of
Chaplygin gas and barotropic fluid with tachyonic field. In the case, when they
have no interaction then both of them retain their own properties. Let us
consider an energy flow between barotropic and tachyonic fluids. In both the
cases we find the exact solutions for the tachyonic field and the tachyonic
potential and show that the tachyonic potential follows the asymptotic
behavior. We have considered an interaction between these two fluids by
introducing a coupling term. Finally, we have considered a model of three
component mixture i.e., mixture of tachyonic field, Chaplygin gas and
barotropic fluid with or without interaction. The coupling functions decays
with time indicating a strong energy flow at the initial period and weak stable
interaction at later stage. To keep the observational support of recent
acceleration we have considered two particular forms (i) Logamediate Scenario
and (ii) Intermediate Scenario, of evolution of the Universe. We have examined
the natures of the recent developed statefinder parameters and slow-roll
parameters in both scenarios with and without interactions in whole evolution
of the universe.Comment: 28 pages, 20 figure
Variable-Speed-of-Light Cosmology from Brane World Scenario
We argue that the four-dimensional universe on the TeV brane of the
Randall-Sundrum scenario takes the bimetric structure of Clayton and Moffat,
with gravitons traveling faster than photons instead, while the radion varies
with time. We show that such brane world bimetric model can thereby solve the
flatness and the cosmological constant problems, provided the speed of a
graviton decreases to the present day value rapidly enough. The resolution of
other cosmological problems such as the horizon problem and the monopole
problem requires supplementation by inflation, which may be achieved by the
radion field provided the radion potential satisfies the slow-roll
approximation.Comment: 18 pages, LaTeX, revised version to appear in Phys. Rev.
One loop renormalization of the four-dimensional theory for quantum dilaton gravity.
We study the one loop renormalization in the most general metric-dilaton
theory with the second derivative terms only. The general theory can be divided
into two classes, models of one are equivalent to conformally coupled with
gravity scalar field and also to general relativity with cosmological term. The
models of second class have one extra degree of freedom which corresponds to
dilaton. We calculate the one loop divergences for the models of second class
and find that the arbitrary functions of dilaton in the starting action can be
fine-tuned in such a manner that all the higher derivative counterterms
disappear on shell. The only structures in both classical action and
counterterms, which survive on shell, are the potential (cosmological) ones.
They can be removed by renormalization of the dilaton field which acquire the
nontrivial anomalous dimension, that leads to the effective running of the
cosmological constant. For some of the renormalizable solutions of the theory
the observable low energy value of the cosmological constant is small as
compared with the Newtonian constant. We also discuss another application of
our result.Comment: 21 pages, latex, no figures
Fine-structure constant variability, equivalence principle and cosmology
It has been widely believed that variability of the fine-structure constant
alpha would imply detectable violations of the weak equivalence principle. This
belief is not justified in general. It is put to rest here in the context of
the general framework for alpha variability [J. D. Bekenstein, Phys. Rev. D 25,
1527 (1982)] in which the exponent of a scalar field plays the role of the
permittivity and inverse permeability of the vacuum. The coupling of particles
to the scalar field is necessarily such that the anomalous force acting on a
charged particle by virtue of its mass's dependence on the scalar field is
cancelled by terms modifying the usual Coulomb force. As a consequence a
particle's acceleration in external fields depends only on its charge to mass
ratio, in accordance with the principle. And the center of mass acceleration of
a composite object can be proved to be independent of the object's internal
constitution, as the weak equivalence principle requires. Likewise the widely
employed assumption that the Coulomb energy of matter is the principal source
of the scalar field proves wrong; Coulomb energy effectively cancels out in the
continuum description of the scalar field's dynamics. This cancellation
resolves a cosmological conundrum: with Coulomb energy as source of the scalar
field, the framework would predict a decrease of alpha with cosmological
expansion, whereas an increase is claimed to be observed. Because of the said
cancellation, magnetic energy of cosmological baryonic matter is the main
source of the scalar field. Consequently the expansion is accompanied by an
increase in alpha; for reasonable values of the framework's sole parameter,
this occurs at a rate consistent with the observers' claims.Comment: RevTeX-4, 22 pages, no figures, added a section on caveats as well as
several new references with discussion of them in body. To appear in Phys.
Rev.
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