Effect of intermediate Minkowskian evolution on CMB bispectrum

Abstract

We consider a non-inflationary early Universe scenario in which relevant scalar perturbations get frozen out at some point, but then are defrosted and follow a long nearly Minkowskian evolution before the hot era. This intermediate stage leaves specific imprint on the CMB 3-point function, largely independent of details of microscopic physics. In particular, the CMB bispectrum undergoes oscillations in the multipole l space with roughly constant amplitude. The latter is in contrast to the oscillatory bispectrum enhanced in the flattened triangle limit, as predicted by inflation with non-Bunch--Davies vacuum. Given this and other peculiar features of the bispectrum, stringent constraints imposed by the Planck data may not apply. The CMB 3-point function is suppressed by the inverse duration squared of the Minkowskian evolution, but can be of observable size for relatively short intermediate Minkowskian stage.

27 pages, 5 figures; references added, representation of the material improved; matches journal version

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• Revisiting constraints on (pseudo)conformal Universe with Planck data
• On holography for (pseudo-)conformal cosmology
• Conformal Universe as false vacuum decay
• Perturbations on and off de Sitter brane in anti-de Sitter bulk