Résumé / Abstract Seminaire_GReCO

"Temporal enhancement of super-horizon curvature perturbations from decays of two curvatons and its cosmological consequences"

T. Suyama

If more than one curvaton dominate the Universe at different epochs from each other, the curvature perturbations can be temporarily enhanced to a value much larger than the observed one 10?5. The traces of the enhancement are left as higher order correlation functions, that is, as non-Gaussianity, the stochastic gravitational waves that are sourced by scalar-scalar mode couplings and the primordial black holes that are formed by the gravitational collapse of the enhanced curvature perturbations. We first confirm that such a temporal enhancement indeed occurs by solving the linearized perturbation equations numerically. We then derive an analytic expression of the full order curvature perturbation which does not rely on the frequently used sudden decay approximation and is exact on super-horizon scales. By using this analytic formula, we provide expressions of the non-linearity parameters fNL, ?NL and gNL. If both two curvatons contribute to the final curvature perturbations, the strong non-Gaussianity appears in the trispectrum rather than in the bispectrum. We also find a unique consistency relation between ?NL and gNL without fNL. By using the second order perturbation theory, we numerically show that the spectrum of the induced gravitational waves has a plateau corresponding to duration of the enhancement and such gravitational waves can be probed by ultimate-DECIGO and space-based atomic interferometers. We finally calculate the abundance of the primordial black holes and put a constraint on the amplitude of the enhanced curvature perturbations.

lundi 8 août 2011 - 11:00
Salle des séminaires Évry Schatzman,
Institut d'Astrophysique de Paris

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