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Published June 4, 2010 | Published
Journal Article Open

Non-Gaussianity from self-ordering scalar fields


The Universe may harbor relics of the post-inflationary epoch in the form of a network of self-ordered scalar fields. Such fossils, while consistent with current cosmological data at trace levels, may leave too weak an imprint on the cosmic microwave background and the large-scale distribution of matter to allow for direct detection. The non-Gaussian statistics of the density perturbations induced by these fields, however, permit a direct means to probe for these relics. Here we calculate the bispectrum that arises in models of self-ordered scalar fields. We find a compact analytic expression for the bispectrum, evaluate it numerically, and provide a simple approximation that may be useful for data analysis. The bispectrum is largest for triangles that are aligned (have edges k_1≃2k_2≃2k_3) as opposed to the local-model bispectrum, which peaks for squeezed triangles (k_1≃k_2≫k_3), and the equilateral bispectrum, which peaks at k_1≃k_2≃k_3. We estimate that this non-Gaussianity should be detectable by the Planck satellite if the contribution from self-ordering scalar fields to primordial perturbations is near the current upper limit.

Additional Information

© 2010 The American Physical Society. Received 2 March 2010; published 4 June 2010. DGF thanks Caltech and CERN for hospitality during the completion of this work. DGF was supported by the Spanish Ministry of Science under Contract No. AP-2005-1092. This work was supported at Caltech by DOE under Contract No. DE-FG03-92-ER40701 and the Gordon and Betty Moore Foundation, and at Dartmouth by NSF under Contract No. AST-0349213.

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