62 research outputs found
Kinetic Axion Dark Matter in String Corrected Gravity
Under the main assumption that the axion scalar field mainly composes the
dark matter in the Universe, in this paper we shall extend the formalism of
kinetic axion gravity to include Gauss-Bonnet terms non-minimally coupled
to the axion field. As we demonstrate, this non-trivial Gauss-Bonnet term has
dramatic effects on the inflationary phenomenology and on the kinetic axion
scenario. Specifically, in the context of our formalism, the kinetic axion
ceases to be kinetically dominated at the end of the inflationary era, since
the condition naturally emerges in the theory. Thus,
unlike the case of kinetic axion gravity, the Gauss-Bonnet corrected
kinetic axion gravity leads to an inflationary era which is not further
extended and the reheating era commences right after the inflationary era,
driven by the fluctuations.Comment: Published in the Physics of the Dark Univers
Growth factor in f(T) gravity
We derive the evolution equation of growth factor for the matter over-dense
perturbation in gravity. For instance, we investigate its behavior in
power law model at small redshift and compare it to the prediction of
CDM and dark energy with the same equation of state in the framework
of Einstein general relativity. We find that the perturbation in gravity
grows slower than that in Einstein general relativity if \p f/\p T>0 due to
the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added,
accepted by JCA
Absorbing hybridization of cobitis taenia and sabanejewia aurata (Cypriniformes, Cobitidae) in water reservoirs of northern Ukraine connected with diploid-polyploid complex formation
Absorbing Hybridization of Cobitis taenia and Sabanejewia aurata (Cypriniformes, Cobitidae)
in Water Reservoirs of Northern Ukraine Connected with Diploid-Polyploid Complex Formation.
Mezhzherin, S. V., Pukhtayevych, P. P., Tsyba, А. А. — In the rivers of the Northern Ukraine by meams
of karyological and allozyme analysys obtained extensive natural hybridization between Cobitis taenia
and Sabanejewia aurata, initially leading to the formation of diploid hybrids. Besides that certain water
bodies are predominantly populated by triploids of the C. taenia — C. tanaitica — S. aurata biotypes.
Since the share of this kind of hybrid biotypes signifi cantly exceeds the number of individuals of S. aurata,
it is concluded that the hybridization of a common and eurybiontic C. taenia with rarer stenobiontic
S. aurata, is of absorbing character
Accelerating universe from F(T) gravity
It is shown that the acceleration of the universe can be understood by
considering a F(T) gravity models. For these F(T) gravity models, a variant of
the accelerating cosmology reconstruction program is developed. Some explicit
examples of F(T) are reconstructed from the background FRW expansion history.Comment: 13 pages, references adde
Pure kinetic k-essence as the cosmic speed-up
In this paper, we consider three types of k-essence. These k-essence models
were presented in the parametric forms. The exact analytical solutions of the
corresponding equations of motion are found. It is shown that these k-essence
models for the presented solutions can give rise to cosmic acceleration.Comment: 10 pages, typos corrected, main results remain the same, minor
changes to match IJTP accepted versio
Einstein-Cartan gravity with scalar-fermion interactions
In this paper, we have considered the g-essence and its particular cases,
k-essence and f-essence, within the framework of the Einstein-Cartan theory. We
have shown that a single fermionic field can give rise to the accelerated
expansion within the Einstein-Cartan theory. The exact analytical solution of
the Einstein-Cartan-Dirac equations is found. This solution describes the
accelerated expansion of the Universe with the equation of state parameter
as in the case of CDM model.Comment: 6 pages, title is change
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