688 research outputs found
Statistical Isotropy of CMB Polarization Maps
We formulate statistical isotropy of CMB anisotropy maps in its most general
form. We also present a fast and orientation independent statistical method to
determine deviations from statistical isotropy in CMB polarization maps.
Importance of having statistical tests of departures from SI for CMB
polarization maps lies not only in interesting theoretical motivations but also
in testing cleaned CMB polarization maps for observational artifacts such as
residuals from polarized foreground emission. We propose a generalization of
the Bipolar Power Spectrum (BiPS) to polarization maps. Application to the
observed CMB polarization maps will be soon possible after the release of WMAP
three year data. As a demonstration we show that for E-polarization this test
can detect breakdown of statistical isotropy due to polarized synchrotron
foreground.Comment: 6 pages, 2 figures, Conclusions & results unchanged; Extension to
cutsky included (discussion & references added); Matches version accepted to
Phys. Rev. D Rapid Com
Odd-Parity Bipolar Spherical Harmonics
Bipolar spherical harmonics (BiPoSHs) provide a general formalism for
quantifying departures in the cosmic microwave background (CMB) from
statistical isotropy (SI) and from Gaussianity. However, prior work has focused
only on BiPoSHs with even parity. Here we show that there is another set of
BiPoSHs with odd parity, and we explore their cosmological applications. We
describe systematic artifacts in a CMB map that could be sought by measurement
of these odd-parity BiPoSH modes. These BiPoSH modes may also be produced
cosmologically through lensing by gravitational waves (GWs), among other
sources. We derive expressions for the BiPoSH modes induced by the weak lensing
of both scalar and tensor perturbations. We then investigate the possibility of
detecting parity-breaking physics, such as chiral GWs, by cross-correlating
opposite parity BiPoSH modes with multipole moments of the CMB polarization. We
find that the expected signal-to-noise of such a detection is modest.Comment: 19 pages, 4 figures, Accepted to PR
Spectroscopy of Cosmic topology
Einstein's theory of gravitation that governs the geometry of space-time, coupled with spectacular advance in cosmological observations, promises to deliver a `standard model' of cosmology in the near future. However, local geometry of space constrains, but does not dictate the topology of the cosmos. hence, Cosmic topology has remained an enigmatic aspect of the `standard model' of cosmology. Recent advance in the quantity and quality of observations has brought this issue within the realm of observational query. The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic consequence of non trivial cosmic topology arising from to the imposed `crystallographic' periodicity on the eigenstates of the Laplacian. The sky maps of Cosmic Microwave Background (CMB) anisotropy and polarization most promising observations that would carry signatures of a violation of statistical isotropy and homogeneity. Hence, a measurable spectroscopy of cosmic topology is made possible using the Bipolar power spectrum (BiPS) of the temperature and polarization that quantifies violation of statistical isotropy
Statistical Isotropy of the Wilkinson Microwave Anisotropy Probe Data: A Bipolar Power Spectrum Analysis
The statistical expectation values of the temperature fluctuations of the
Cosmic Microwave Background (CMB) are assumed to be preserved under rotations
of the sky. We investigate the Statistical Isotropy (SI) of the CMB anisotropy
maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using
Bipolar Power Spectrum (BiPS) proposed in [Hajian & Souradeep 2003]. The method
can probe specific regions in multipole space using appropriate window
functions. The BiPS is estimated for full sky CMB anisotropy maps based on the
first year WMAP data using a range of window functions. The BiPS spectra
computed for both full sky maps for all our window functions are consistent
with zero, roughly within . The null BiPS results may be interpreted
as an absence of strong violation of statistical isotropy in the first-year
WMAP data on angular scales larger than that corresponding to .
However, pending a careful direct comparison, our results do not necessarily
conflict with the specific SI related anomalies reported using other
statistical tests.Comment: 5 pages, 4 figures, trimmed in size, results and conclusions
unchanged, matches version to appear in ApJ. Let
Testing Global Isotropy of Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Data: Temperature Analysis
We examine statistical isotropy of large scale anisotropies of the Internal Linear Combination (ILC) map, based on three year WMAP data. Our study reveals no significant deviation from statistical isotropy on large angular scales of 3-year ILC map. Comparing statistical isotropy of 3-year ILC map and 1-year ILC map, we find a significant improvement in 3-year ILC map which can be due to the gain model, improved ILC map processing and foreground minimization
Dipole leakage and low CMB multipoles
A number of studies of WMAP-7 have highlighted that the power at the low multipoles in CMB power spectrum is lower than their theoretically predicted value. Angular correlation between the orientations of these low multipoles have also been discovered. While these observations may have cosmological ramification, it is important to investigate possible observational artifacts that can mimic them. The CMB dipole, which is much higher than the quadrupole, can get leaked to the higher multipoles due to the non-circular beam of the CMB experiment. In this paper, an analytical method has been developed and simulations are carried out to study the effect of the non-circular beam on power leakage from the dipole. It has been shown that the small, but non-negligible power from the dipole can get transferred to the quadrupole and the higher multipoles due to the non-circular beam. Simulations have also been carried out for Planck scan strategy, and comparative results between WMAP and Planck have been presented
Statistical Isotropy violation of the CMB brightness fluctuations
Certain anomalies at large angular scales in the cosmic microwave background
measured by WMAP have been suggested as possible evidence of breakdown of
statistical isotropy(SI). Most CMB photons free-stream to the present from the
surface of last scattering. It is thus reasonable to expect statistical
isotropy violation in the CMB photon distribution observed now to have
originated from SI violation in the baryon-photon fluid at last scattering, in
addition to anisotropy of the primordial power spectrum studied earlier in
literature.
We consider the generalized anisotropic brightness distribution fluctuations,
(at conformal time ) in contrast to the
SI case where it is simply a function of and . The brightness fluctuations expanded in Bipolar Spherical Harmonic
(BipoSH) series, can then be written as where terms encode deviations from statistical isotropy. We
study the evolution of from
non-zero terms at last
scattering. Similar to the SI case, power at small spherical harmonic (SH)
multipoles of at the last
scattering, is transferred to at
larger SH multipoles. The structural similarity is more apparent in the
asymptotic expression for large values of the final SH multipoles. This
formalism allows an elegant identification of any SI violation observed today
to a possible origin in the SI violation present in the baryon-photon fluid
(eg., due to the presence of significant magnetic field).Comment: 14 pages, 4 figures, added illustrative example of SI violation in
baryon-photon fluid, matches version accepted for publication in Phys. Rev.
Galactic Foreground Constraints from the Python V Cosmic Microwave Background Anisotropy Data
We constrain Galactic foreground contamination of the Python V cosmic
microwave background anisotropy data by cross correlating it with foreground
contaminant emission templates. To model foreground emission we use 100 and 12
m dust emission templates and two point source templates based on the PMN
survey. The analysis takes account of inter-modulation correlations in 8
modulations of the data that are sensitive to a large range of angular scales
and also densely sample a large area of sky. As a consequence the analysis here
is highly constraining. We find little evidence for foreground contamination in
an analysis of the whole data set. However, there is indication that
foregrounds are present in the data from the larger-angular-scale modulations
of those Python V fields that overlap the region scanned earlier by the UCSB
South Pole 1994 experiment. This is an independent consistency cross-check of
findings from the South Pole 1994 data.Comment: 15 pages, 1 figure, ApJ accepted versio
Estimation of Primordial Spectrum with post-WMAP 3 year data
In this paper we implement an improved (error sensitive) Richardson-Lucy
deconvolution algorithm on the measured angular power spectrum from the WMAP 3
year data to determine the primordial power spectrum assuming different points
in the cosmological parameter space for a flat LCDM cosmological model. We also
present the preliminary results of the cosmological parameter estimation by
assuming a free form of the primordial spectrum, for a reasonably large volume
of the parameter space. The recovered spectrum for a considerably large number
of the points in the cosmological parameter space has a likelihood far better
than a `best fit' power law spectrum up to \Delta \chi^2_{eff} \approx -30. We
use Discrete Wavelet Transform (DWT) for smoothing the raw recovered spectrum
from the binned data. The results obtained here reconfirm and sharpen the
conclusion drawn from our previous analysis of the WMAP 1st year data. A sharp
cut off around the horizon scale and a bump after the horizon scale seem to be
a common feature for all of these reconstructed primordial spectra. We have
shown that although the WMAP 3 year data prefers a lower value of matter
density for a power law form of the primordial spectrum, for a free form of the
spectrum, we can get a very good likelihood to the data for higher values of
matter density. We have also shown that even a flat CDM model, allowing a free
form of the primordial spectrum, can give a very high likelihood fit to the
data. Theoretical interpretation of the results is open to the cosmology
community. However, this work provides strong evidence that the data retains
discriminatory power in the cosmological parameter space even when there is
full freedom in choosing the primordial spectrum.Comment: 13 pages, 4 figures, uses Revtex4, new analysis and results,
references added, matches version accepted to Phys. Rev.
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