2005 (IPP)

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    Statistical isotropy of CMB anisotropy from WMAP
    (2005-02-01) Souradeep, Tarun; Hajian, Amir
    The statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003. The Bipolar Power Spectrum (BiPS) is estimated for the full sky CMB anisotropy maps of the first year WMAP data. The method allows us to isolate regions in multipole space and study each region independently. This search shows no evidence for violation of statistical isotropy in the first-year WMAP data on angular scales larger than that corresponding to l ≈ 60 .
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    CMB Anisotropy Due to Tangled magnetic fields in re-ionized models
    (2005-04-01) Seshadri, T. R.; Subramanian, Kandaswamy
    Primordial tangled cosmological Magnetic Fields source rotational velocity perturbations of the baryon fluid, even in the post-recombination universe. These vortical modes inturn leave a characteristic imprint on the temperature anisotropy of the Cosmic Microwave Background (CMB), if the CMB photons can be re-scatterred after recombination. Observations from WMAP in- dicate that the Universe underwent a relatively early re-ionization (zri ∼ 15), which does indeed lead to a significant optical depth for re-scattering of CMB photons after the re-ionization epoch. We compute the resulting additional temperature anisotropies, induced by primordial magnetic fields in the postrecombination universe. We show that in models with early re-ionization, a nearly scale-invariant spectrum of tangled magnetic fields which redshift to a present value of B0 ∼ 3 × 10−9 Gauss, produce vector mode perturbations which in turn induce additional temperature anisotropy of about 0.3 to 0.4 µK over very small angular scales, with l upto ∼ 10000 or so.98.62.En, 98.70.Vc, 98.80.Cq, 95.30.Qd