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          Institute: MPI für Astrophysik     Collection: Cosmology     Display Documents

ID: 12136.0, MPI für Astrophysik / Cosmology
Measurement of the cosmic microwave background bispectrum on the COBE DMR sky maps
Authors:Komatsu, E.; Wandelt, B. D.; Spergel, D. N.; Banday, A. J.; Gorski, K. M.
Date of Publication (YYYY-MM-DD):2002
Title of Journal:The Astrophysical Journal
Journal Abbrev.:Astrophys. J.
Issue / Number:1
Start Page:19
End Page:29
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:We measure the angular bispectrum of the cosmic microwave background (CMB) radiation anisotropy from the COBE Differential Microwave Radiometer (DMR) 4 yr sky maps. The angular bispectrum is the harmonic transform of the three-point correlation function, analogous to the angular power spectrum, the harmonic transform of the two-point correlation function. First, we study statistical properties of the bispectrum and the normalized bispectrum. We find the latter more useful for statistical analysis; the distribution of the normalized bispectrum is very much Gaussian, while the bare bispectrum distribution is highly non-Gaussian. Then, we measure 466 modes of the normalized bispectrum, all independent combinations of three-point configurations up to a maximum multipole of 20, the mode corresponding to the DMR beam size. By measuring 10 times as many modes as the sum of previous work, we test the Gaussianity of the DMR maps. We compare the data with the simulated Gaussian realizations, finding no significant detection of the normalized bispectrum on a mode-by-mode basis. We also find that the previously reported detection of the normalized bispectrum is consistent with a statistical fluctuation. By fitting a theoretical prediction to the data for the primordial CMB bispectrum, which is motivated by slow- roll inflation, we put a weak constraint on the parameter characterizing nonlinearity in inflation. Simultaneously fitting the foreground bispectra estimated from interstellar dust and synchrotron template maps shows that neither dust nor synchrotron emission significantly contributes to the bispectrum at high Galactic latitude. We conclude that the DMR map is consistent with Gaussianity.
Free Keywords:cosmic microwave background; cosmology : observations; early universe
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astrophysik
External Affiliations:Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA; Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA; Tohoku Univ, Inst Astron, Aoba Ku, Sendai, Miyagi 9808578, Japan; Princeton Univ, Dept Phys, Princeton, NJ 08544 USA; Inst Adv Study, Sch Nat Sci, Princeton, NJ 08540 USA; Max Planck Inst Astrophys, D-85740 Garching, Germany; European So Observ, D-85740 Garching, Germany; Univ Warsaw Observ, PL-00478 Warsaw, Poland
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