593 research outputs found

### Cosmological Alfv\'en waves in the recent CMB data, and the observational bound on the primordial vector perturbation

In the presence of the primordial magnetic field, initial vector (vorticity)
perturbations produce cosmological Alfven waves and leave imprints on cosmic
microwave background (CMB) temperature and polarization anisotropy. We have
investigated imprints of cosmological Alfven waves in CMB anisotropy. For data
constraints, we have used the power spectrum of the recent CMB observations,
and correlations estimated from WMAP Internal Linear Combination (ILC) maps.
Our analysis shows 3 sigma evidence of cosmological Alfven waves. Using the 3
sigma limit from our analysis and the Alfven velocity limit from the total
energy density constraint, we impose a lower bound on the amplitude of
primordial vector perturbation: 4*10^-12 at k_0=0.002/Mpc.Comment: v2: change in analysis method and confidence interval improved v3:
typos corrected v4: a typo in Eq. 36 corrected v5: lower bound on vector
perturbation in more compliant form for ease of comparison, references adde

### Lack of angular correlation and odd-parity preference in CMB data

We have investigated the angular correlation in the recent CMB data. In
addition to the known large-angle correlation anomaly, we find the lack of
correlation at small angles with high statistical significance. We have
investigated various non-cosmological contamination and additionally WMAP
team's simulated data. However, we have not found a definite cause. In the
angular power spectrum of WMAP data, there exist anomalous odd-parity
preference at low multipoles. Noting the equivalence between the power spectrum
and the correlation, we have investigated the association between the lack of
large-angle correlation and the odd-parity preference. From our investigation,
we find that the odd-parity preference at low multipoles is, in fact, a
phenomenological origin of the lack of large-angle correlation. Futher
investigation is required to find out whether the origin of the anomaly is
cosmological or due to unaccounted systematics. The data from Planck surveyor,
which has systematics distinct from the WMAP, will greatly help us to resolve
its origin.Comment: v3: typos corrected, v4: plots updated, v5: analysis extended, v6:
matched with the accepted version in ApJ (minor change

### CMB data constraint on self-annihilation of dark matter particles

Recently, self-annihilation of dark matter particles is proposed to explain
the "WMAP Haze" and excess of energetic positrons and electrons in ATIC and
PAMELA results. If self-annihilation of dark matter occurs around the
recombination of cosmic plasma, energy release from self-annihilation of dark
matter delays the recombination, and hence affects CMB anisotropy. By using the
recent CMB data, we have investigated the self-annihilation of dark matter
particles. In this investigation, we do not find statistically significant
evidence, and impose an upper bound on / m_chi. The upcoming data
from Planck surveyor and the Fermi Gamma-ray telescope will allow us to break
some of parameter degeneracy and improve constraints on self-annihilation of
dark matter particles.Comment: a talk presented at the Invisible Universe International Conference
at the Palais de l'UNESCO, Paris, v2: references adde

### Parametric tension between even and odd multipole data of WMAP power spectrum: unaccounted contamination or missing parameters?

There exist power contrast in even and odd multipoles of WMAP power spectrum
at low and intermediate multipole range. This anomaly is explicitly associated
with the angular power spectrum, which are heavily used for cosmological model
fitting. Having noted this, we have investigated whether even(odd) multipole
data set is consistent with the WMAP concordance model. Our investigation shows
WMAP concordance model does not make a good fit for even(odd) multipole data
set, and there exist tension between two data subsets. Noting tension is
highest in primordial power spectrum parameters, we have additionally
considered a running spectral index, but find tension increases to even a
higher level. We believe these parametric tensions may be indications of
unaccounted contamination or imperfection of the model.Comment: v2: Latex error fixed, v3: matched with the accepted version in ApJL,
conclusion unchange

### Combined multi-frequency map for point source substraction

A method is proposed for combining multi-frequency maps in order to produce a
catalogue of extragalactic point sources using data from future high-precision
satellite experiments. We have found the optimal way for combining maps at
different frequencies in order to maximize the signal (point sources) to noise
(rest of the signal) ratio. Our approach is a natural multi-frequency
generalization of the band-pass filter introduced by Tegmark and de
Oliveira-Costa (1998). We show that combination of different frequency maps
gives us the possibility of creating a more complete catalogue of point
sources

### Critical points of the cosmic velocity field and the uncertainties in the value of the Hubble constant

The existence of critical points for the peculiar velocity field is a natural
feature of the correlated vector field. These points appear at the junctions of
velocity domains with different orientations of their averaged velocity
vectors. Since peculiar velocities are the important cause of the scatter in
the Hubble expansion rate, we propose that a more precise determination of the
Hubble constant can be made by restricting analysis to a subsample of
observational data containing only the zones around the critical points of the
peculiar velocity field, associated with voids and saddle points. On
large-scales the critical points, where the first derivative of the
gravitational potential vanishes, can easily be identified using the density
field and classified by the behavior of the Hessian of the gravitational
potential. We use high-resolution N-body simulations to show that these regions
are stable in time and hence are excellent tracers of the initial conditions.
Furthermore, we show that the variance of the Hubble flow can be substantially
minimized by restricting observations to the subsample of such regions of
vanishing velocity instead of aiming at increasing the statistics by averaging
indiscriminately using the full data sets, as is the common approach.Comment: 17 pages, 6 figures and 2 tables, minor modifications after receiving
several useful comment

### Symmetry and anti-symmetry of the CMB anisotropy pattern

Given an arbitrary function, we may construct symmetric and antisymmetric
functions under a certain operation. Since statistical isotropy and homogeneity
of our Universe has been a fundamental assumption of modern cosmology, we do
not expect any particular symmetry or antisymmetry in our Universe. Besides
fundamental properties of our Universe, we may also figure our contamination
and improve the quality of the CMB data products, by matching the unusual
symmetries and antisymmetries of the CMB data with known contaminantions.
Noting this, we have investigated the symmetry and antisymmetry of CMB
anisotropy pattern, which provides the deepest survey. If we let the operation
to be a coordinate inversion, the symmetric and antisymmetric functions have
even and odd-parity respectively. The investigation on the parity of the recent
CMB data shows a large-scale odd-parity preference, which is very unlikely in
the statistical isotropic and homogeneous Universe. We have investigated the
association of the WMAP systematics with the anomaly, but not found a definite
non-cosmological cause. Additionally, we have investigated the phase of even
and odd multipole data respectively, and found the behavior distinct from each
other. Noting the odd-parity preference anomaly, we have fitted a cosmological
model respectively to even and odd multipole data, and found significant
parametric tension. Besides anomalies explicitly associated with parity, there
are anomalous lack of large-scale correlation in CMB data. Noting the
equivalence between the power spectrum and the correlation, we have
investigated the association between the lack of large-angle correlation and
the odd-parity preference of the angular power spectrum. From our analysis, we
find that the odd-parity preference at low multipoles is, in fact,
phenomenologically identical with the lack of large-angle correlation.Comment: review articl

### 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

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