2003 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/626

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Author: search.filters.author.Souradeep, Tarun

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    Primordial power spectrum from WMAP
    (2011-07-05) Shafieloo, Arman; Souradeep, Tarun
    The observed angular power spectrum of the cosmic microwave background temperature anisotropy, Cl, is a convolution of a cosmological radiative transport kernel with an assumed primordial power spectrum of inhomogeneities. Exquisite measurements of Cl over a wide range of multipoles from the Wilkinson Microwave Anisotropy Probe (WMAP) has opened up the possibility to deconvolve the primordial power spectrum for a given set of cosmological parameters (base model). We implement an improved (error sensitive) Richardson-Lucy deconvolution algorithm on the measured angular power spectrum from WMAP assuming the concordance cosmological model. The most prominent feature of the recovered P(k) is a sharp, infrared cutoff on the horizon scale. The resultant Cl spectrum using the recovered spectrum has a likelihood far better than a scale invariant, or, “best fit” scale free spectra (ΔlnL≈25 with respect to Harrison Zeldovich, and, ΔlnL≈11 with respect to power law with ns=0.95). The recovered P(k) has a localized excess just above the cutoff which leads to great improvement of likelihood over the simple monotonic forms of model infrared cutoff spectra considered in the post WMAP literature. The recovered P(k), in particular, the form of infrared cutoff is robust to small changes in the cosmological parameters. We show that remarkably similar form of infrared cutoff is known to arise in very reasonable extensions and refinements of the predictions from simple inflationary scenarios. Our method can be extended to other cosmological observations such as the measured matter power spectrum and, in particular, the much awaited polarization spectrum from WMAP.
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    Statistical isotropy of the cosmic microwave background
    (2011-07-05) Souradeep, Tarun; Hajian, Amir
    The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra large scale structure of the cosmos, in particular, of non trivial cosmic topol- ogy. The statistical isotropy (SI) of the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even be- yond the cosmic horizon. We propose a set of measures, κℓ (ℓ = 1, 2, 3, . . .) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. We numerically compute the predicted κℓ spectra for CMB anisotropy in flat torus universe models. Characteristic signature of different models in the κℓ spectrum are noted.
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    Statistical isotropy of CMB and cosmic topology
    (2011-07-05) Hajian, Amir; Souradeep, Tarun
    The breakdown of statistical homogeneity and isotropy of cosmic perturbations is a generic feature of ultra large scale structure of the cosmos, in particular, of non trivial cosmic topology. The statisti- cal isotropy (SI) of the Cosmic Microwave Background temperature fluctuations (CMB anisotropy) is sensitive to this breakdown on the largest scales comparable to, and even beyond the cosmic hori- zon. We study a set of measures, κℓ (ℓ = 1, 2, 3, . . .) which for non-zero values indicate and quantify statistical isotropy violations in a CMB map. The main goal here is to interpret the κℓ spectrum and relate it to characteristic patterns in the correlation function of CMB anisotropy arising from cosmic topology. We numerically compute the predicted κℓ spectrum for CMB anisotropy in flat torus universe models. The essential features are captured in the leading order approximation to the correlation function where κℓ can be calculated analytically. The κℓ spectrum is shown to reflect the number, importance and relative orientation of principal directions in the CMB correlation dictated by the shape of the Dirichlet domain (DD) of the compact space and its size relative to cosmic horizon. Hence, besides detecting cosmic topology, κℓ can discriminate between different topology of the universe complementing ongoing search for cosmic topology in CMB anisotropy data.
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    Measuring statistical isotropy of the CMB anisotropy
    (2003-07-05) Ajian, Amir; Souradeep, Tarun
    The statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. This assumption of statistical isotropy (SI) of the CMB anisotropy should be observationally verified since detection of violation of SI could have profound implications for cosmology. We propose a set of measures, κℓ (ℓ = 1, 2, 3, . . .) for detecting violation of statistical isotropy in an observed CMB anisotropy sky map indicated by non zero κℓ. We define an estimator for the κℓ spectrum and ana- lytically compute its cosmic bias and cosmic variance. The results match those obtained by measuring κℓ using simulated sky maps. Non-zero (bias corrected) κℓ larger than the SI cosmic variance will imply violation of SI. The SI mea- sure proposed in this paper is an appropriate statistics to investigate preliminary indication of SI violation in the recently released WMAP data.