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Published December 15, 2008 | Published
Journal Article Open

A hemispherical power asymmetry from inflation


Measurements of cosmic microwave background temperature fluctuations by the Wilkinson Microwave Anisotropy Probe indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a multifield inflationary theory, the curvaton model, can produce this power asymmetry without violating the homogeneity constraint. The mechanism requires the introduction of a large-amplitude superhorizon perturbation to the curvaton field, possibly a preinflationary remnant or a superhorizon curvaton-web structure. The model makes several predictions, including non-Gaussianity and modifications to the inflationary consistency relation, that will be tested with forthcoming cosmic microwave background experiments.

Additional Information

© 2008 The American Physical Society. Received 3 June 2008; revised 10 July 2008; published 16 December 2008. We thank K. Górski and H. K. Eriksen for discussions. This work was supported by DOE Grant No. DE-FG03-92-ER40701 and the Gordon and Betty Moore Foundation.

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