51 research outputs found
What Happened if Dirac, Sciama and Dicke had Talked to Each Other About Cosmology?
The inspiring contributions to cosmology originating from the above named researchers seem abandoned today. Surprisingly, their basic ideas can be realized by slight modifications of each proposal. We study Dirac's article on the large number hypothesis (1938), Sciama's proposal of realizing Mach's principle (1953), and Dicke's scalar theory of gravitation with a variable speed of light (1957). Dicke's tentative theory can be formulated in a way which is compatible with Sciama's hypothesis on the gravitational constant G. Additionally, such a cosmological model satisfies Dirac's large number hypothesis (LNH) without entailing a visible time dependence of G which never has been verified, though originally predicted by Dirac. While Dicke's proposal in first approximation agrees with the classical tests of GR, the cosmological redshift arises from a shortening of measuring rods rather than an expansion of space. The speed of light turns out to be the increase of the horizon R. A related discussion is given in arxiv:0708.3518
A gauge theoretic approach to elasticity with microrotations
We formulate elasticity theory with microrotations using the framework of
gauge theories, which has been developed and successfully applied in various
areas of gravitation and cosmology. Following this approach, we demonstrate the
existence of particle-like solutions. Mathematically this is due to the fact
that our equations of motion are of Sine-Gordon type and thus have soliton type
solutions. Similar to Skyrmions and Kinks in classical field theory, we can
show explicitly that these solutions have a topological origin.Comment: 15 pages, 1 figure; revised and extended version, one extra page;
revised and extended versio
Notes on Theories
The cosmological models based on teleparallel gravity with nonzero torsion
are considered. To investigate the evolution of this theory, we consider the
phase-space analysis of the theory. It shows when the tension scalar can
be written as an inverse function of where
and , the system is an autonomous one. Furthermore,the
phase analysis is given out. We perform the dynamical
analysis for the models and particularly. We find that the universe will
settle into de-Sitter phase for both models. And we have examined the evolution
behavior of the power law form in the plane.Comment: 13 pages, 2 figure
Observational Constraints on Teleparallel Dark Energy
We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations
(BAO), and Cosmic Microwave Background (CMB) observations to constrain the
recently proposed teleparallel dark energy scenario based on the teleparallel
equivalent of General Relativity, in which one adds a canonical scalar field,
allowing also for a nonminimal coupling with gravity. Using the power-law, the
exponential and the inverse hyperbolic cosine potential ansatzes, we show that
the scenario is compatible with observations. In particular, the data favor a
nonminimal coupling, and although the scalar field is canonical the model can
describe both the quintessence and phantom regimes.Comment: 19 pages, 6 figures, version accepted by JCA
Phase-Space analysis of Teleparallel Dark Energy
We perform a detailed dynamical analysis of the teleparallel dark energy
scenario, which is based on the teleparallel equivalent of General Relativity,
in which one adds a canonical scalar field, allowing also for a nonminimal
coupling with gravity. We find that the universe can result in the
quintessence-like, dark-energy-dominated solution, or to the stiff dark-energy
late-time attractor, similarly to standard quintessence. However, teleparallel
dark energy possesses an additional late-time solution, in which dark energy
behaves like a cosmological constant, independently of the specific values of
the model parameters. Finally, during the evolution the dark energy
equation-of-state parameter can be either above or below -1, offering a good
description for its observed dynamical behavior and its stabilization close to
the cosmological-constant value.Comment: 23 pages, 4 figures, 5 tables, version published at JCA
On the gravitodynamics of moving bodies
In the present work we propose a generalization of Newton's gravitational
theory from the original works of Heaviside and Sciama, that takes into account
both approaches, and accomplishes the same result in a simpler way than the
standard cosmological approach. The established formulation describes the local
gravitational field related to the observables and effectively implements the
Mach's principle in a quantitative form that retakes Dirac's large number
hypothesis. As a consequence of the equivalence principle and the application
of this formulation to the observable universe, we obtain, as an immediate
result, a value of Omega = 2. We construct a dynamic model for a galaxy without
dark matter, which fits well with recent observational data, in terms of a
variable effective inertial mass that reflects the present dynamic state of the
universe and that replicates from first principles, the phenomenology proposed
in MOND. The remarkable aspect of these results is the connection of the effect
dubbed dark matter with the dark energy field, which makes it possible for us
to interpret it as longitudinal gravitational waves.Comment: 18 pages, 4 figures. Final version: almost identical to the reference
journal; Cent. Eur. J. Phys. 201
Maximal symmetry and metric-affine f(R) gravity
The affine connection in a space-time with a maximally symmetric spatial
subspace is derived using the properties of maximally symmetric tensors. The
number of degrees of freedom in metric-affine gravity is thereby considerably
reduced while the theory allows spatio-temporal torsion and remains non-metric.
The Ricci tensor and scalar are calculated in terms of the connection and the
field equations derived for the Einstein-Hilbert as wells as for f(R)
Lagrangians. By considering specific forms of f(R), we demonstrate that the
resulting Friedmann equations in Palatini formalism without torsion and
metric-affine formalism with maximal symmetry are in general different in the
presence of matter.Comment: 7 page
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