Browsing by Author "Rotti, Aditya"

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    A comparison of CMB lensing e ciency of gravitational waves and large scale structure
    (IUCAA, 2015-02) Padmanabhan, Hamsa; Rotti, Aditya; Tarun, Sauradeep
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    A New Window into Stochestic Gravitational Wave Background
    (2013-09-20) Rotti, Aditya; Souradeep, Tarun
    A stochastic gravitational wave background (SGWB) would gravitationally lens the cosmic mi- crowave background (CMB) photons. We correct the results provided in existing literature for modi cations to the CMB polarization power spectra due to lensing by gravitational waves (GW). Weak lensing by gravitational waves (GW) distorts all the four CMB power spectra, however its e ect is most striking in the mixing of power between the E-mode and B-mode of CMB polarization. This suggests the possibility of using measurements of the CMB angular power spectra to constrain the energy density ( GW) of the SGWB. Using current data sets (QUAD, WMAP and ACT), we nd that the most stringent constraints on the present GW come from measurements of the angular power spectra of CMB temperature anisotropies. In near future more stringent bounds on GW can be expected with improved upper limits on the B-modes of CMB polarization. Any detection of B-modes of CMB polarization above the expected signal from large scale structure(LSS) lensing could be a signal for a SGWB
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    Statistical isotropy violation in WMAP CMB maps due to non-circular beams
    (IUCAA, 2015-02) Das, Santanu; Mitra, Sanjit; Rotti, Aditya
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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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    WMAP anomaly : Weak lensing in disguise
    (IUCAA, 2015-02) Rotti, Aditya; Aich, Moumita; Souradeep, Tarun