571 research outputs found
Cross-correlation of the CMB and foregrounds phases derived from the WMAP data
We present circular and linear cross-correlation tests and the
"friend-of-friend" analysis for phases of the Internal Linear Combination Map
(ILC) and the WMAP foregrounds for all K--W frequency bands at the range of
multipoles . We compare also Tegmark, de Oliveira-Costa and
Hamilton (2003) and Naselsky et al. (2003) cleaned maps with corresponding
foregrounds. We have found significant deviations from the expected Poissonian
statistics for all the cleaned maps and foregrounds. Our analysis shows that,
for a low multipole range of the cleaned maps, power spectra contains some of
the foregrounds residuals mainly from the W band.Comment: 11 pages, 10 figures. Submitted to MNRA
Bulk Viscosity, Decaying Dark Matter, and the Cosmic Acceleration
We discuss a cosmology in which cold dark-matter particles decay into
relativistic particles. We argue that such decays could lead naturally to a
bulk viscosity in the cosmic fluid. For decay lifetimes comparable to the
present hubble age, this bulk viscosity enters the cosmic energy equation as an
effective negative pressure. We investigate whether this negative pressure is
of sufficient magnitude to account fo the observed cosmic acceleration. We show
that a single decaying species in a flat, dark-matter dominated cosmology
without a cosmological constant cannot reproduce the observed
magnitude-redshift relation from Type Ia supernovae. However, a delayed bulk
viscosity, possibly due to a cascade of decaying particles may be able to
account for a significant fraction of the apparent cosmic acceleration.
Possible candidate nonrelativistic particles for this scenario include sterile
neutrinos or gauge-mediated decaying supersymmetric particles.Comment: 7 pages, 4 figure
Ionization history of the cosmic plasma in the light of the recent CBI and future PLANCK data
The paper is devoted to the methods of determination of the cosmological
parameters from recent CMB observations. We show that the more complex models
of kinetics of recombination with a few "missing" parameters describing the
recombination process provide better agreement between measured and expected
characteristics of the CMB anisotropy. In particular, we consider the external
sources of the Ly-{alpha} and Ly-{c} radiation and the model with the strong
clustering of baryonic component. These factors can constrain the estimates of
the cosmological parameters usually discussed. We demonstrate also that the
measurements of polarization can improve these estimates and, for the precision
expected for the PLANCK mission, allow to discriminate a wide class of models.Comment: 25 pages, 7 figures, extended and corrected after the referee report.
Accepted in Ap
On the Possibility of Anisotropic Curvature in Cosmology
In addition to shear and vorticity a homogeneous background may also exhibit
anisotropic curvature. Here a class of spacetimes is shown to exist where the
anisotropy is solely of the latter type, and the shear-free condition is
supported by a canonical, massless 2-form field. Such spacetimes possess a
preferred direction in the sky and at the same time a CMB which is isotropic at
the background level. A distortion of the luminosity distances is derived and
used to test the model against the CMB and supernovae (using the Union
catalog), and it is concluded that the latter exhibit a higher-than-expected
dependence on angular position. It is shown that future surveys could detect a
possible preferred direction by observing ~ 20 / (\Omega_{k0}^2) supernovae
over the whole sky.Comment: Extended SNe analysis and corrected some CMB results. Text also
extended and references added. 8 pages, 5 figure
The Caustic Ring Model of the Milky Way Halo
We present a proposal for the full phase space distribution of the Milky Way
halo. The model is axially and reflection symmetric and its time evolution is
self-similar. It describes the halo as a set of discrete dark matter flows with
stated densities and velocity vectors everywhere. We first discuss the general
conditions under which the time evolution of a cold collisionless
self-gravitating fluid is self-similar, and show that symmetry is not necessary
for self-similarity. When spherical symmetry is imposed, the model is the same
as described by Fillmore and Goldreich, and by Bertschinger, twenty-three years
ago. The spherically symmetric model depends on one dimensionless parameter
and two dimensionful parameters. We set = 0.3, a value
consistent with the slope of the power spectrum of density perturbations on
galactic scales. The dimensionful parameters are determined by the Galactic
rotation velocity (220 km/s) at the position of the Sun and by the age of the
Galaxy (13.7 Gyr). The properties of the outer caustics are derived in the
spherically symmetric model. The structure of the inner halo depends on the
angular momentum distribution of the dark matter particles. We assume that
distribution to be axial and reflection symmetric, and dominated by net overall
rotation. The inner caustics are rings whose radii are determined in terms of a
single additional parameter . We summarize the observational
evidence in support of the model. The evidence is consistent with
= 0.18 in Concordance Cosmology, equivalent to = 0.26 in
Einstein - de Sitter cosmology. We give formulas to estimate the flow densities
and velocity vectors anywhere in the Milky Way halo. The properties of the
first forty flows at the location of the Earth are listed.Comment: 35 pages, 6 figure
Cosmological Co-evolution of Yang-Mills Fields and Perfect Fluids
We study the co-evolution of Yang-Mills fields and perfect fluids in Bianchi
type I universes. We investigate numerically the evolution of the universe and
the Yang-Mills fields during the radiation and dust eras of a universe that is
almost isotropic. The Yang-Mills field undergoes small amplitude chaotic
oscillations, which are also displayed by the expansion scale factors of the
universe. The results of the numerical simulations are interpreted analytically
and compared with past studies of the cosmological evolution of magnetic fields
in radiation and dust universes. We find that, whereas magnetic universes are
strongly constrained by the microwave background anisotropy, Yang-Mills
universes are principally constrained by primordial nucleosynthesis and the
bound is comparatively weak, and Omega_YM < 0.105 Omega_rad.Comment: 13 pages, 5 figures, submitted to PR
Late Decaying Dark Matter, Bulk Viscosity and the Cosmic Acceleration
We discuss a cosmology in which cold dark matter begins to decay into
relativistic particles at a recent epoch (z < 1). We show that the large
entropy production and associated bulk viscosity from such decays leads to an
accelerating cosmology as required by observations. We investigate the effects
of decaying cold dark matter in a Lambda = 0, flat, initially matter dominated
cosmology. We show that this model satisfies the cosmological constraint from
the redshift-distance relation for type Ia supernovae. The age in such models
is also consistent with the constraints from the oldest stars and globular
clusters. Possible candidates for this late decaying dark matter are suggested
along with additional observational tests of this cosmological paradigm.Comment: 8 pages, 3 figures, 1 tabl
Interior of Distorted Black Holes
We study the interior of distorted static axisymmetric black holes. We obtain
a general interior solution and study its asymptotics both near the horizon and
singularity. As a special example, we apply the obtained results to the case of
the so-called `caged' black holes.Comment: 12 pages, 16 figure
Geometry and Statistics of Cosmic Microwave Polarization
Geometrical and statistical properties of polarization of CMB are analyzed.
Singular points of the vector field which describes CMB polarization are found
and classified. Statistical distribution of the singularities is studied. A
possible signature of tensor perturbations in CMB polarization is discussed.
For a further analysis of CMB statistics Minkowski functionals are used, which
present a technically simple method to search for deviations from a Gaussian
distribution.Comment: 37 pages, 5 figures, submitted in Int.J.Mod.Phys.
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