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 Relic gravity waves from Braneworld inflation(2001-10-02) Sahni, Varun; Sami, M.; Souradeep, TarunWe discuss a scenario in which extra dimensional effects allow a scalar field with a steep potential to play the dual role of the inflaton as well as dark energy (quintessence). The post-inflationary evo- lution of the universe in this scenario is generically characterised by a ‘kinetic regime’ during which the kinetic energy of the scalar field greatly exceeds its potential energy resulting in a ‘stiff’ equa- tion of state for scalar field matter Pφ ≃ ρφ. The kinetic regime precedes the radiation dominated epoch and introduces an important new feature into the spectrum of relic gravity waves created quantum mechanically during inflation. The amplitude of the gravity wave spectrum increases with wavenumber for wavelengths shorter than the comoving horizon scale at the commencement of the radiative regime. This ‘blue tilt’ is a generic feature of models with steep potentials and imposes strong constraints on a class of inflationary braneworld models. Prospects for detection of the grav- ity wave background by terrestrial and space-borne gravity wave observatories such as LIGO II and LISA are discussed.Item Window function for non-circular beam CMB anisotropy experiment(2001-07-05) Souradeep, Tarun; Ratra, BharatWe develop computationally rapid methods to compute the window function for a cosmic microwave background anisotropy experiment with a non-circular beam which scans over large angles on the sky. To concretely illustrate these methods we compute the window function for the Python V experiment which scans over large angles on the sky with an elliptical Gaussian beam.Item 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.