Browsing by Author "Kamionkowski, Marc"

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    Odd-parity bipolar spherical harmonics
    (2011-09-13) Book, Laura G.; Kamionkowski, Marc; Souradeep, Tarun
    Bipolar spherical harmonics (BiPoSHs) provide a general formalism for quantifying departures in the cosmic microwave background (CMB) from statistical isotropy (SI) and from Gaussianity. However, prior work has focused only on BiPoSHs with even parity. Here we show that there is another set of BiPoSHs with odd parity, and we explore their cosmological applications. We describe systematic artifacts in a CMB map that could be sought by measurement of these odd-parity BiPoSH modes. These BiPoSH modes may also be produced cosmologically through lensing by gravitational waves (GWs), among other sources. We derive expressions for the BiPoSH modes induced by the weak lensing of both scalar and tensor perturbations. Our estimate of the expected signal-to-noise with which we could measure the weak lensing of GWs from the correlation of two BiPoSH modes is respectable, indicating that such a measurement may be merited. We also investigate the possibility to detect parity-breaking physics, such as chiral GWs, by cross-correlating opposite parity BiPoSH modes with multipole moments of the CMB polarization. We nd that the expected signal-to-noise of such a detection is modest, with errors dominated by cosmic variance.
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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.