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Title: Anisotropic power spectrum and bispectrum in the f(Φ)F² mechanism

A suitable coupling of the inflaton φ to a vector kinetic term F² gives frozen and scale invariant vector perturbations. We compute the cosmological perturbations ζ that result from such coupling by taking into account the classical vector field that unavoidably gets generated at large scales during inflation. This generically results in a too-anisotropic power spectrum of ζ. Specifically, the anisotropy exceeds the 1% level (10% level) if inflation lasts ~5 e-folds (~50 e-folds) more than the minimal amount required to produce the cosmic microwave background modes. This conclusion applies, among others, to the application of this mechanism for magnetogenesis, for anisotropic inflation, and for the generation of anisotropic perturbations at the end of inflation through a waterfall field coupled to the vector (in this case, the unavoidable contribution that we obtain is effective all throughout inflation, and it is independent of the waterfall field). For a tuned duration of inflation, a 1% (10%) anisotropy in the power spectrum corresponds to an anisotropic bispectrum which is enhanced like the local one in the squeezed limit, and with an effective local fNL~3(~30). More in general, a significant anisotropy of the perturbations may be a natural outcome of all models that sustainmore » higher than 0 spin fields during inflation.« less
Authors:
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Publication Date:
OSTI Identifier:
1102652
Type:
Publisher's Accepted Manuscript
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 87; Journal Issue: 2; Journal ID: ISSN 1550-7998
Publisher:
American Physical Society
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English