Generating cosmological perturbations at Horndeski bounce

Abstract

We construct a concrete model of Horndeski bounce with strong gravity in the past. Within this model we show that the correct spectra of cosmological perturbations may be generated at early contracting epoch, with mild fine-tuning ensuring that the scalar spectral tilt n S and tensor-to-scalar ratio r are consistent with observations. The smallness of r is governed by the smallness of the scalar sound speed. Arbitrarily small values of r are forbidden in our setup because of the strong coupling in the past. Nevertheless, we show that it is possible to generate perturbations in a controllable way, i.e. in the regime where the background evolution and perturbations are legitimately described within classical field theory and weakly coupled quantum theory.

Parity violation in primordial tensor non-Gaussianities from matter bounce cosmology

“…To clarify this point, let us follow refs. [86][87][88][89][90][91][92]. In terms of the canonically normalized tensor fluctuation v ij = aM p h ij /2 denoted by v below, one obtains…”

Physics news on the Internet (based on electronic preprints)

“…The obtained models are stable, and the perturbations above the background in them are not superluminal. In their new paper [3], Yu A Ageeva, P K Petrov, and V A Rubakov have substantially developed and justified this class of models. They show that cosmological primordial perturbations can be generated in them with a spectrum which is necessary for galaxy formation and is observed in relic radiation perturbations.…”

“…They show that cosmological primordial perturbations can be generated in them with a spectrum which is necessary for galaxy formation and is observed in relic radiation perturbations. It is interesting that perturbations in model [3] are generated at the stage of previous compression before the contemporary expansion. Thus, it was shown that the Universe may have evolved in nontrivial ways, and, being consistent with the observational data, the new wide class of cosmological models is admissible.…”