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CMB B-mode polarization from Thomson scattering in the local universe

Hirata, Christopher M. and Loeb, Abraham and Afshordi, Niayesh (2005) CMB B-mode polarization from Thomson scattering in the local universe. Physical Review D, 71 (6). Art. No. 063531. ISSN 1550-7998.

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The polarization of the cosmic microwave background (CMB) is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the dominant CMB polarization created by density perturbations at the times of recombination and reionization because it generates both E and B polarization modes, whereas the density perturbations create only E polarization. The limits of our ability to measure gravitational waves are thus determined by statistical and systematic errors from CMB experiments, foregrounds, and nonlinear evolution effects such as gravitational lensing of the CMB. Usually it is assumed that most foregrounds can be removed because of their frequency dependence, however Thomson scattering of the CMB quadrupole by electrons in the Galaxy or nearby structures shares the blackbody frequency dependence of the CMB. If the optical depth from these nearby electrons is anisotropic, the polarization generated can include B modes even if no tensor perturbations are present. We estimate this effect for the Galactic disk and nearby extragalactic structures, and find that it contributes to the B polarization at the level of ~(1–2)×10^-4 µK per logarithmic interval in multipole ℓ for ℓ<30. This is well below the detectability level even for a future CMB polarization satellite and hence is negligible. Depending on its structure and extent, the Galactic corona may be a source of B-modes comparable to the residual large-scale lensing B-mode after the latter has been cleaned using lensing reconstruction techniques. For an extremely ambitious post-Planck CMB experiment, Thomson scattering in the Galactic corona is thus a potential contaminant of the gravitational wave signal; conversely, if the other foregrounds can be cleaned out, such an experiment might be able to constrain models of the corona.

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Hirata, Christopher M.0000-0002-2951-4932
Additional Information:© 2005 The American Physical Society. (Received 11 January 2005; published 29 March 2005) We thank Joseph Taylor and Bob Benjamin for useful conversations about the Galactic electron density, and Nikhil Padmanabhan for his assistance with the E=B decomposition software. C.H. is supported by NASA NGT5-50383. This work was supported in part by NSF grants AST-0204514, AST-0071019 and NASA Grant No. NAG 5-13292 (for A.L.). Some of the results in this paper have been derived using the HEALPIX [33] package. We acknowledge the use of the Legacy Archive for Microwave Background Data Analysis (LAMBDA) [41]. Support for LAMBDA is provided by the NASA Office of Space Science.
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NASANAG 5-13292
Subject Keywords:gravitational waves; gravitational lenses; radiofrequency cosmic radiation; cosmology; galaxies
Record Number:CaltechAUTHORS:HIRprd05a
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ID Code:11100
Deposited By: Archive Administrator
Deposited On:15 Jul 2008 03:09
Last Modified:17 May 2017 21:59

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