Gravity seminar - Marco Bruni Seminar

Abstract: In the first part of this talk I will give an overview of work on nonlinear structure formation in ΛCDM in the context of General Relativity (GR). Starting from briefly presenting a post-Friedmann approximation, I will show how gravito-magnetic effects (AKA frame-dragging) can be extracted from standard Newtonian N-body simulations, as well as from N-body simulations with GRAMSES, a GR code. I will then present full-GR simulations of a toy-model “cosmic web” of over-densities voids and filaments with the Einstein Toolkit fluid code, showing how the first shell-crossing at peaks of over-densities is very well predicted by the simple top hat model, while in the formation of the cosmic web a role is played by gravito-magnetism, especially around filaments. In the second part of the talk I will move on more speculative ground, illustrating the qualitative nonlinear dynamics of universe models with two interacting dark components, some form of dark energy and cold dark matter (CDM), showing how an initial singularity can be avoided and the Universe can instead emerge from an unstable vacuum, or bouncing off the same vacuum in the case of positive curvature, with a late evolution dominated by CDM and, eventually, a stable vacuum, a scenario in agreement with observations.