2010 (IPP)

Permanent URI for this collectionhttp://localhost:4000/handle/11007/152

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Author: search.filters.author.Souradeep, TarunHas files: Yes

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    Perturbed power-law parameters from WMAP7
    (2010-11-19) Minu, Joy; Souradeep, Tarun
    We present a perturbative approach for studying inflation models with soft departures from scale free spectra of the power law model. In the perturbed power law (PPL) approach one obtains at the leading order both the scalar and tensor power spectra with the running of their spectral indices, in contrast to the widely used slow roll expansion. The PPL spectrum is confronted data and we show that the PPL parameters are well estimated from WMAP-7 data.
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    Odd-parity CMB bispectrum
    (2010-10-22) Kamionkowski, Marc; Souradeep, Tarun
    Measurement of the cosmic microwave background (CMB) bispectrum, or three-point correlation function, has now become one of the principle efforts in early-Universe cosmology. Here we show that there is a odd-parity component of the CMB bispectrum that has been hitherto unexplored. We argue that odd-parity temperature-polarization bispectra can arise, in principle, through weak lensing of the CMB by chiral gravitational waves or through cosmological birefringence, although the signals will be small even in the best-case scenarios. Measurement of these bispectra requires only modest modifications to the usual data-analysis algorithms. They may be useful as a consistency test in searches for the usual bispectrum and to search for surprises in the data.
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    Statistical isotropy violation of the CMB brightness fluctuations
    (2010-03-22) Aich, Moumita; Souradeep, Tarun
    Certain anomalies at large angular scales in the cosmic microwave background measured by WMAP have been suggested as possible evidence of breakdown of statistical isotropy(SI). SI violation of cosmological perturbations is a generic feature of ultra large scale structure of the cosmos and breakdown of global symmetries. Most CMB photons free-stream to the present from the surface of last scattering. It is thus reasonable to expect statistical isotropy violation in the CMB photon distribution observed now to have originated from SI violation in the baryon-photon fluid at last scattering, in addition to anisotropy of the primordial power spectrum studied earlier in literature. We consider the generalized anisotropic brightness distribution fluctuations, ∆(~ k, ˆ n, τ ) (at con-formal time τ ) in contrast to the SI case where it is simply a function of |~ k| and ˆ k ˆ n. The brightness fluctuations expanded in Bipolar Spherical Harmonic (BipoSH) series, can then be written as ∆LM ℓ1ℓ2 (k, τ ) where L > 0 terms encode deviations from statistical isotropy. Violation of SI encoded in the present off-diagonal elements of the harmonic space correlation haℓmaℓ′m′ i, equivalently, the BipoSH coefficients ALM ℓℓ′ , are then related to the generalized BipoSH brightness fluctuation terms at present. We study the evolution of ∆LM ℓ1ℓ2 (k, τ ) from non-zero terms ∆LM ℓ3ℓ4 (k, τs) at last scattering, in the free streaming regime. We show that the terms with given BipoSH multipole, LM, evolve independently. Moreover, similar to the SI case, power at small spherical harmonic (SH) multipoles of ∆LM ℓ3ℓ4 (k, τs) at the last scattering, is transferred to ∆LM ℓ1ℓ2 (k, τ ) at larger SH multipoles. The structural similarity is more apparent in the asymptotic expression for large values of the final SH multipoles. This formalism allows an elegant identification of any SI violation observed today to a possible origin in SI violating physics present in the baryon-photon fluid. This is illustrated for the known result of SI violating angular correlations due to the presence of a homogeneous magnetic field in the baryon-photon fluid.
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    Size of the longest filament in the luminous red galaxy distribution
    (2010-09-12) Souradeep, Tarun
    Filaments are one of the most prominent features visible in the galaxy distribution. Considering the Luminous Red Galaxies (LRGs) in the Sloan Digital Sky Survey Data Release Seven (SDSS DR7), we have analyzed the filamentarity in 11 nearly two dimensional (2D) sections through a volume limited subsample of this data. The galaxy distribution, we find, has excess filamentarity in comparison to a random distribution of points. We use a statistical technique “Shuffle” to determine LMAX, the largest length-scale at which we have statistically significant filaments. We find that LMAX varies in the range 100−130 h−1Mpc across the 11 slices, with a mean value LMAX = 110 ± 12 h−1Mpc. Longer filaments, though possibly present in our data, are not statistically significant and are the outcome of chance alignments.
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    Power spectrum nulls due to non-standard inflationary evolution
    (2010-12-30) Goswami, Gaurav; Souradeep, Tarun
    The simplest models of inflation based on slow roll produce nearly scale invariant primordial power spectra (PPS). But there are also numerous models that predict radically broken scale invariant PPS. In particular, markedly cuspy dips in the PPS correspond to nulls where the perturbation amplitude, hence PPS, goes through a zero at a specific wavenumber. Near this wavenumber, the true quantum nature of the generation mechanism of the primordial fluctuations may be revealed. Naively these features may appear to arise from fine tuned initial conditions. However, we show that this behavior arises under fairly generic set of conditions involving super-Hubble scale evolution of perturbation modes during inflation. We illustrate this with the well-studied examples of punctuated inflation and the Starobinsky-break model.