2005 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/443

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Author: search.filters.author.Souradeep, Tarun

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Now showing 1 - 5 of 5
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    Statistical isotropy of CMB anisotropy from WMAP
    (2005-02-01) Souradeep, Tarun; Hajian, Amir
    The statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003. The Bipolar Power Spectrum (BiPS) is estimated for the full sky CMB anisotropy maps of the first year WMAP data. The method allows us to isolate regions in multipole space and study each region independently. This search shows no evidence for violation of statistical isotropy in the first-year WMAP data on angular scales larger than that corresponding to l ≈ 60 .
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    Post-WMAP Assessment of Infrared cutoff in the Primordial Spectrum from Inflation
    (2005-08-01) Sinha, Rita; Souradeep, Tarun
    The recent Cosmic Microwave Background (CMB) measurements indicate that there is power deficiency of the CMB anisotropies at large scales compared with the ΛCDM model. We have investigated the possibility of explaining such effects by a class of primordial power spectra which have infrared cutoffs close to the horizon scale. The primordial power spectrum recovered by direct deconvolution of the observed CMB angular spectrum indicates that the data prefers a sharp infrared cutoff with a localized excess (bump) just above the cutoff. We have been motivated to assess plausible extensions of simplest inflationary scenarios which readily accommodate similar form of infrared cutoff. We carry out a complete Bayesian analysis of the parameter space using Markov Chain Monte Carlo technique with such a class of primordial power spectra. We show that primordial power spectrum that have features such as an infrared cutoff followed by a subsequent excess in power give better fit to the observed data compared to a nearly scale-invariant power law or power spectrum with just a monotonic infrared cutoff. However, there is substantial room for improvement in the match to data and calls for exploration of other mechanisms that may lead to infrared cutoff even closer to that recovered by direct deconvolution approach.
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    Estimating Cosmological Parameters from CMBR : Systematic effects
    (2005-01-01) Sinha, Rita; Souradeep, Tarun
    The fluctuations in the cosmic microwave background radiation depend on the cosmological parameters. We carry out Markov Chain Monte Carlo simulations to constrain the cosmological parameter space with the current CMB data for possible systematic effects! such as beam noncircularity in CMB measurements and incomplete sky coverage.
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    Cosmic microwave background bipolar power spectrum: Basic formalism and applications
    (2005-01-01) Hajian, Amir; Souradeep, Tarun
    We study the statistical isotropy (SI) of temperature fluctuations of the CMB as dis- tinct from Gaussianity. We present a detailed formalism of the bipolar power spectrum BiPS) which was introduced as a fast method of measuring the statistical isotropy by Hajian & Souradeep 2003. The method exploits the existence of patterns in the real space correlations of the CMB temperature field. We discuss the applications of BiPS in constraining the topology of the universe and other theoretical scenarios of SI violation. Unlike the traditional methods of search for cosmic topology, this method is computationally fast. We also show that BiPS is potentially a good tool to detect the effect of observational artifacts in a CMB map such as non-circular beam, anisotropic noise, etc. Our method has been successfully applied to the Wilkinson Microwave Anisotropy Probe sky maps by Hajian et al. 2004, but no strong evidence of SI violation was found.
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    Blind estimation of the power spectrum of CMB anisotropy from WMAP
    (2005-06-01) Saha, Rajib; Jain, Pankaj; Souradeep, Tarun
    Accurate measurements of angular power spectrum of Cosmic Microwave Background (CMB) radiation has lead to marked improvement in the estimates of different cosmological parameters. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. We present the estimation of CMB angular power spectrum from the multi-frequency observations ofWMAP using a novel model-independent method. The primary product of WMAP are the observations of CMB in 10 independent difference assemblies (DA) that have uncorrelated noise. Our method utilizes maximum information available within WMAP data by linearly combining all the DA maps to remove foregrounds and estimating the power spectrum from cross power spectra of clean maps with independent noise. We compute 24 cross power spectra which are the basis of the final power spectrum. The binned average power matches with WMAP team’s published power spectrum closely. A small systematic difference at large multipoles is accounted for by the correction for the expected residual power from unresolved point sources. The correction is small and significantly tempered. Previous estimates have depended on foreground templates built using extraneous observational input. This is the first demonstration that the CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data.