25 research outputs found
Genesis of Dark Energy: Dark Energy as Consequence of Release and Two-stage Tracking Cosmological Nuclear Energy
Recent observations on Type-Ia supernovae and low density () measurement of matter including dark matter suggest that the present-day
universe consists mainly of repulsive-gravity type `exotic matter' with
negative-pressure often said `dark energy' (). But the nature
of dark energy is mysterious and its puzzling questions, such as why, how,
where and when about the dark energy, are intriguing. In the present paper the
authors attempt to answer these questions while making an effort to reveal the
genesis of dark energy and suggest that `the cosmological nuclear binding
energy liberated during primordial nucleo-synthesis remains trapped for a long
time and then is released free which manifests itself as dark energy in the
universe'. It is also explained why for dark energy the parameter . Noting that for stiff matter and for radiation; is for dark energy because is due to `deficiency of
stiff-nuclear-matter' and that this binding energy is ultimately released as
`radiation' contributing , making . When
dark energy is released free at , . But as on present day
at when radiation strength has diminished to , . This, thus almost solves the dark-energy mystery of
negative pressure and repulsive-gravity. The proposed theory makes several
estimates /predictions which agree reasonably well with the astrophysical
constraints and observations. Though there are many candidate-theories, the
proposed model of this paper presents an entirely new approach (cosmological
nuclear energy) as a possible candidate for dark energy.Comment: 17 pages, 4 figures, minor correction
The averaged tensors of the relative energy-momentum and angular momentum in general relativity and some their applications
There exist at least a few different kind of averaging of the differences of
the energy-momentum and angular momentum in normal coordinates {\bf NC(P)}
which give tensorial quantities. The obtained averaged quantities are
equivalent mathematically because they differ only by constant scalar
dimensional factors. One of these averaging was used in our papers [1-8] giving
the {\it canonical superenergy and angular supermomentum tensors}.
In this paper we present another averaging of the differences of the
energy-momentum and angular momentum which gives tensorial quantities with
proper dimensions of the energy-momentum and angular momentum densities. But
these averaged relative energy-momentum and angular momentum tensors, closely
related to the canonical superenergy and angular supermomentum tensors, {\it
depend on some fundamental length }.
The averaged relative energy-momentum and angular momentum tensors of the
gravitational field obtained in the paper can be applied, like the canonical
superenergy and angular supermomentum tensors, to {\it coordinate independent}
analysis (local and in special cases also global) of this field.
We have applied the averaged relative energy-momentum tensors to analyze
vacuum gravitational energy and momentum and to analyze energy and momentum of
the Friedman (and also more general) universes. The obtained results are very
interesting, e.g., the averaged relative energy density is {\it positive
definite} for the all Friedman universes.Comment: 30 pages, minor changes referring to Kasner universe
Bianchi Type V Viscous Fluid Cosmological Models in Presence of Decaying Vacuum Energy
Bianchi type V viscous fluid cosmological model for barotropic fluid
distribution with varying cosmological term is investigated. We have
examined a cosmological scenario proposing a variation law for Hubble parameter
in the background of homogeneous, anisotropic Bianchi type V space-time.
The model isotropizes asymptotically and the presence of shear viscosity
accelerates the isotropization. The model describes a unified expansion history
of the universe indicating initial decelerating expansion and late time
accelerating phase. Cosmological consequences of the model are also discussed.Comment: 10 pages, 3 figure
How does Inflation Depend Upon the Nature of Fluids Filling Up the Universe in Brane World Scenario
By constructing different parameters which are able to give us the
information about our universe during inflation,(specially at the start and the
end of the inflationary universe) a brief idea of brane world inflation is
given in this work. What will be the size of the universe at the end of
inflation,i.e.,how many times will it grow than today's size is been speculated
and analysed thereafter. Different kinds of fluids are taken to be the matter
inside the brane. It is observed that in the case of highly positive pressure
grower gas like polytropic,the size of the universe at the end of inflation is
comparitively smaller. Whereas for negative pressure creators (like chaplygin
gas) this size is much bigger. Except thse two cases, inflation has been
studied for barotropic fluid and linear redshift parametrization too. For them the size of the universe after
inflation is much more high. We also have seen that this size does not depend
upon the potential energy at the end of the inflation. On the contrary, there
is a high impact of the initial potential energy upon the size of inflation.Comment: 20 page
Stability analysis of agegraphic dark energy in Brans-Dicke cosmology
Stability analysis of agegraphic dark energy in Brans-Dicke theory is
presented in this paper. We constrain the model parameters with the
observational data and thus the results become broadly consistent with those
expected from experiment. Stability analysis of the model without best fitting
shows that universe may begin from an unstable state passing a saddle point and
finally become stable in future. However, with the best fitted model, There is
no saddle intermediate state. The agegraphic dark energy in the model by itself
exhibits a phantom behavior. However, contribution of cold dark matter on the
effective energy density modifies the state of teh universe from phantom phase
to quintessence one. The statefinder diagnosis also indicates that the universe
leaves an unstable state in the past, passes the LCDM state and finally
approaches the sable state in future.Comment: 15 pages, 12 figure
Plane-symmetric inhomogeneous magnetized viscous fluid universe with a variable
The behavior of magnetic field in plane symmetric inhomogeneous cosmological
models for bulk viscous distribution is investigated. The coefficient of bulk
viscosity is assumed to be a power function of mass density . The values of cosmological constant for these models are
found to be small and positive which are supported by the results from recent
supernovae Ia observations. Some physical and geometric aspects of the models
are also discussed.Comment: 18 pages, LaTex, no figur
Variable G and : scalar-tensor versus RG-improved cosmology
We study the consequences due to time varying and in
scalar-tensor theories of gravity for cosmology, inspired by the modifications
introduced by the Renormalization Group (RG) equations in the Quantum Einstein
Gravity. We assume a power-law scale factor in presence contemporarily of both
the scalar field and the matter components of the cosmic fluid, and analyze a
special case and its generalization, also showing the possibility of a phantom
cosmology. In both such situations we find a negative kinetic term for the
scalar field and, possibly, an equation-of-state parameter . A
violation of dominant energy condition (DEC) for is also possible in both
of them; but, while in the first special case the -energy density then
remains positive, in the second one we find it negative.Comment: 25 pages, to be published in Gen. Rel. Grav. 200
Transient Crossing of Phantom divide line under Gauss-Bonnet interaction
Smooth double crossing of the phantom barrier has been
found possible in cosmological model with Gauss-Bonnet-scalar interaction, in
the presence of background cold dark matter. Such crossing has been observed to
be a sufficiently late time phenomena and independent of the sign of
Gauss-Bonnet-scalar interaction. The luminosity distance versus redshift curve
shows a perfect fit with the model up to .Comment: 9 pages, 9 figure