NeBRiC · Non-linear effects and backreaction in classical and quantum cosmology

Cosmology has gone through an amazing revolution during the last decade owing to the large amount of new precise observational data. These data strongly indicate the existence of two periods of accelerated expansion in the history of the Universe. One in the primordial universe,the so-called inflationary phase, and one at the present era. The link between data and models is made mostly by linear perturbation theory on a spatially homogeneous and isotropic Friedmann Universe. But beyond linear order many interesting effects appear, such as the non-Gaussianity, that should be present in the CMB, and backreaction (BR) effects. In particular, quantum BR of primordial fluctuations can significantly modify the dynamics of the early universe and its observational signatures, while classical BR of large scale structure (LSS) might contribute to the observed late time acceleration. The goal of my project is to quantify these non-linear effects more precisely. First, I want to connect the BR of the LSS to observations using a light-cone averaging prescription. Then, I want to evaluate BR effects from magnetic fields generated during inflation in a consistent way both using the effective equation for the cosmological backreaction andthe data inside the backward light-cone of a physical observer. I also plan to obtain observationalbounds on BR from the study of the effective equation of state it induces and from its effect on early phases of expansion, from preheating to CMB decoupling passing through the relativistic era that takes place before the Big-bang nucleosynthesis. Also an alternative approach compared to the BR of the LSS will be then considered, I will investigate how a smooth expand Universe can be obtained from small, static inhomogeneous cells that are glued together. This possibility is more challenging and almost unexplored. Finally, I want to investigate how non-Gaussianity (and other observables) can change as consequences of the loop corrections.