IUCAA Preprints
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Item WMAP anomaly : Weak lensing in disguise(IUCAA, 2015-02) Rotti, Aditya; Aich, Moumita; Souradeep, TarunItem Dipole leakage and low CMB multipoles(IUCAA, 2015-02) Das, Santanu; Souradeep, TarunItem SCOPE: An e cient method of Cosmological Parameter Estimation(IUCAA, 2015-02) Das, Santanu; Souradeep, TarunItem Quantum effects near a point mass in 2+1 dimensional gravity(2014-11-26) Souradeep, Tarun; Sahni, VarunItem Generation of seed perturbations from quantum cosmology(2014-11-26) Souradeep, TarunThe origin of seed perturbations in the Universe is studied within the framework of a specific mini super space model. It is shown that the ‘creation’ of the Universe as a result of a quantum transition from a flat empty space time would lead to a flat FLRW (Friedmann Lemaitre Robertson- Walker) Universe with weak inhomogeneous perturbations at large wavelengths. The power spectrum of these perturbations is found to be scale invariant at horizon crossing (i.e., the Harrison- Zeldovich spectrum). It is also recognised that the seed perturbations generated in our model would be generically of the isocurvature kind.Item Density perturbations, gravity waves and the cosmic microwave background(2014-07-30) Souradeep, Tarun; Sahni, VarunItem A New Window into Stochestic Gravitational Wave Background(2013-09-20) Rotti, Aditya; Souradeep, TarunA 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 SGWBItem OVRO CMB anisotropy measurement constraints on flat - ^ and open CDM cosmogonies(2012-03-13) Mukherjee, Pia; Souradeep, Tarun; Ratra, Bharat; et al.We use Owens Valley Radio Observatory (OVRO) cosmic microwave backgroun (CMB) anisotropy data to constrain cosmological parameters. We account for th OVRO beamwidth and calibration uncertainties, as well as the uncertainty induced b the removal of non-CMB foreground contamination. We consider open and spatially flat-Λ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω0 the range 0.1–1, baryonic-mass density parameter ΩB in the range (0.005–0.029)h− and age of the universe t0 in the range (10–20) Gyr. Marginalizing over all paramete but Ω0, the OVRO data favors an open (spatially-flat-Λ) model with Ω0 ≃ 0.33 (0.1 At the 2 σ confidence level model normalizations deduced from the OVRO data a mostly consistent with those deduced from the DMR, UCSB South Pole 1994, Pytho I-III, ARGO, MAX 4 and 5, White Dish, and SuZIE data sets.Item Primordial power spectrum from WMAP(2011-07-05) Shafieloo, Arman; Souradeep, TarunThe 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.Item Statistical isotropy of the cosmic microwave background(2011-07-05) Souradeep, Tarun; Hajian, AmirThe 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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