29 research outputs found
Century of
The cosmological constant was proposed 100 years ago in order to make the
model of static Universe, imagined then by most scientists, possible. Today it
is the main candidate for the physical essence causing the observed accelerated
expansion of our Universe. But, as well as a hundred years ago, its nature is
unknown. This paper is devoted to the story of invention of by Albert
Einstein in 1917, rejection of it by him in 1931 and returning of it into the
science by other scientists during the century.Comment: 14 pages, accepted for publication in Europ. Phys. J.
Tachyonic fields in cosmology
The possibility of explanation of accelerated expansion of the Universe by
tachyonic scalar fields which homogeneously fill the world is discussed. The
dependences of potential and kinetic term on scale factor are deduced for the
case of quintessential and phantom dark energy with generalized linear
barotropic equation of state. The possibility to distinguish the tachyonic
scalar field as dark energy from other scalar field models, especially from
classical scalar field, is analyzed.Comment: 12 pages (v1,v2 in Ukrainian, v3 in English), 4 figures; accepted for
publication in Collected Physical Papers of Shevchenko Scientific Societ
Evolution of density and velocity profiles of matter in large voids
We analyse the evolution of cosmological perturbations which leads to the
formation of large voids in the distribution of galaxies. We assume that
perturbations are spherical and all components of the Universe - radiation,
matter and dark energy - are continuous media with ideal fluid energy-momentum
tensors, which interact only gravitationally. Equations of the evolution of
perturbations in the comoving to cosmological background reference frame for
every component are obtained from equations of conservation and Einstein's ones
and are integrated by modified Euler method. Initial conditions are set at the
early stage of evolution in the radiation-dominated epoch, when the scale of
perturbation is mush larger than the particle horizon. Results show how the
profiles of density and velocity of matter in spherical voids with different
overdensity shells are formed.Comment: 9 figure
Do the cosmological observational data prefer phantom dark energy?
The dynamics of expansion and large scale structure formation of the Universe
are analyzed for models with dark energy in the form of a phantom scalar field
which initially mimics a -term and evolves slowly to the Big Rip
singularity. The discussed model of dark energy has three parameters -- the
density and the equation of state parameter at the current epoch,
and , and the asymptotic value of the equation of state parameter at
, . Their best-fit values are determined jointly
with all other cosmological parameters by the MCMC method using observational
data on CMB anisotropies and polarization, SNe Ia luminosity distances, BAO
measurements and more. Similar computations are carried out for CDM
and a quintessence scalar field model of dark energy. It is shown that the
current data slightly prefer the phantom model, but the differences in the
maximum likelihoods are not statistically significant. It is also shown that
the phantom dark energy with monotonically increasing density in future will
cause the decay of large scale linear matter density perturbations due to the
gravitational domination of dark energy perturbations long before the Big Rip
singularity.Comment: 13 pages, 8 figures, 5 tables; comments and references added; version
accepted for publication in Phys.Rev.