Browsing by Author "Joshi, Nidhi"

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    Bipolar Harmonic encoding of CMB correlation patterns
    (2009-12-01) Joshi, Nidhi; Jhingan, S.; Souradeep, Tarun; et al.
    Deviations from statistical isotropy can be modeled in various ways, for instance, anisotropic cosmological models (Bianchi models), compact topologies and presence of primordial magnetic field. Signature of anisotropy manifests itself in CMB correlation patterns. Here we explore the symmetries of the correlation function and its implications on the observable measures constructed within the Bipolar harmonic formalism for these variety of models. Different quantifiers within the Bipolar harmonic representation are used to distinguish between plausible models of breakdown of statistical isotropy and as a spectroscopic tool for discriminating between distinct cosmic topology.
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    Revealing Non-circular beam effect in WMAP-7 CMB maps with BipoSH measures of Statistical Isotropy
    (IUCAA, 2015-02) Joshi, Nidhi; Das, Santanu; Mitra, Sanjit
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    Statistics of bipolar representation of CMB maps
    (2011-09-04) Joshi, Nidhi; Rotti, Aditya; Souradeep, Tarun
    Gaussianity of temperature fluctuations in the Cosmic Microwave Background(CMB) implies that the statistical properties of the temperature field can be completely characterized by its two point correlation function. The two point correlation function can be expanded in full generality in the bipolar spherical harmonic(BipoSH) basis. Looking for significant deviations from zero for Bipolar Spherical Harmonic(BipoSH) Coefficients derived from observed CMB maps forms the basis of the strategy used to detect isotropy violation. In order to quantify ”significant deviation” we need to understand the distributions of these coefficients. We analytically evaluate the moments and the distribution of the coefficients of expansion(ALM l1l2 ), using characteristic function approach. We show that for BipoSH coefficients with M = 0 an analytical form for the moments up to any arbitrary order can be derived. For the remaining BipoSH coefficients with M = 0, the moments derived using the characteristic function approach need to be supplemented with a correction term. The correction term is found to be important particularly at low multipoles. We provide a general prescription for calculating these corrections, however we restrict the explicit calculations only up to kurtosis. We confirm our results with measurements of BipoSH coefficients on numerically simulated statistically isotropic CMB maps.
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    Statistics of statistical anisotropy measures
    (2011-08-11) Joshi, Nidhi