Abstract
We investigate the bounce realization in the framework of
DHOST cosmology, focusing on the relation with observables. We
perform a detailed analysis of the scalar and tensor perturbations
during the Ekpyrotic contraction phase, the bounce phase, and the
fast-roll expansion phase, calculating the power spectra, the
spectral indices and the tensor-to-scalar ratio. Furthermore, we
study the initial conditions, incorporating perturbations generated
by Ekpyrotic vacuum fluctuations, by matter vacuum fluctuations, and
by thermal fluctuations. The scale invariance of the scalar power
spectrum can be acquired introducing a matter contraction phase
before the Ekpyrotic phase, or invoking a thermal gas as the
source. The DHOST bounce scenario with cosmological perturbations
generated by thermal fluctuations proves to be the most efficient
one, and the corresponding predictions are in perfect agreement with
observational bounds. Especially the tensor-to-scalar ratio is many
orders of magnitude within the allowed region, since it is
suppressed by the Hubble parameter at the beginning of the bounce phase.