10,465 research outputs found
Oscillating Friedman Cosmology
The non-singular, oscillating Friedman cosmology within the framework of
General Relativity is considered. The general oscillatory solution given in
terms of elliptic functions and the conditions for its existence are discussed.
It is shown that the wall-like-matter and the small, but negative cosmological
constant are required for oscillations. The oscillations can , in principle, be
deep enough to allow standard hot universe processes like recombination and
nucleosynthesis. It is shown that the wall-like-matter and string-like-matter
can be interpreted as scalar fields with some potentials. This may give another
candidate for the dark matter which may be compatible with observational data.
For an exact elementary oscillatory solution it is shown that the associated
scalar field potential is oscillating as well.Comment: Latex file, 27 pages, figures available on reques
Phantom Dark Energy and its Cosmological Consequences
I discuss the dark energy characterized by the violation of the null energy
condition (), dubbed phantom. Amazingly, it is admitted by
the current astronomical data from supernovae. We discuss both classical and
quantum cosmological models with phantom as a source of matter and present the
phenomenon called phantom duality.Comment: 3 pages, MG11 conference proceeding
Extended Uncertainty Principle for Rindler and cosmological horizons
We find exact formulas for the Extended Uncertainty Principle (EUP) for the
Rindler and Friedmann horizons and show that they can be expanded to obtain
asymptotic forms known from the previous literature. We calculate the
corrections to Hawking temperature and Bekenstein entropy of a black hole in
the universe due to Rindler and Friedmann horizons. The effect of the EUP is
similar to the canonical corrections of thermal fluctuations and so it rises
the entropy signalling further loss of information.Comment: 7 pages, 6 figures, REVTEX 4.1, minor changes, refs update
Redshift drift in varying speed of light cosmology
We derive a redshift drift formula within the framework of varying speed of
light (VSL) theory using the specific ansatz for the variability of . We show that negative values of the parameter , which correspond to
diminishing value of the speed of light during the evolution of the universe,
effectively rescales dust matter to become little negative pressure matter, and
the cosmological constant to became phantom. Positive values of (growing
) make VSL model to become more like Cold Dark Matter (CDM) model.
Observationally, there is a distinction between the VSL model and the
CDM model for the admissible values of the parameter , though it will be rather difficult to detect by planned extremely
large telescopes (E-ELT, TMT, GMT) within their accuracy.Comment: 4 pages, 1 figure, title and body changed to match a published
version on redshift drift onl
Exotic-singularity-driven dark energy
We discuss various types of exotic (non-standard) singularities in the
Universe: a Big-Rip (BR or type I), a Sudden Future Singularity (SFS or type
II), a Generalized Sudden Future Singularity, a Finite Scale Factor singularity
(FSF or type III), a Big-Separation (BS or type IV) and a -singularity. They
are characterized by violation of all or some of the energy conditions which
results in a blow-up of all or some of the physical quantities: the scale
factor, the energy density, the pressure, and the barotropic index. We relate
the emergence of these singularities with physical theories (superstring,
brane, higher-order gravity, loop quantum cosmology). We show how the models
involving exotic singularities may serve as dark energy by applying the
observational data. In particular, we show that some of these exotic
singularities (though being of a weak type according to relativistic
definitions) may occur in the near future of the universe.Comment: 10 pages, 9 figures, contribution to "Invisible Universe", paris
29.06-3.07.09, to appear in AIP Conference Proceeding
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