Our next cosmology seminar takes place on Friday 19th of November, seminar room E349 at 2pm. The speaker is Danilo Artigas from the Institut d’Astrophysique Spatiale (Paris, France) and Quantum Cosmos Lab (Cracow, Poland).
At 14:00, room E349, Danilo Artigas (IAS), will be talking about
Hamiltonian formalism for cosmological perturbations: the separate-universe approach
In order to describe inhomogeneities and anisotropies in the Universe, one generally considers a Friedmann-Lemaître-Robertson-Walker background and introduces perturbations on top of it. Such a method is commonly used in Lagrangian formalism and is fundamental for example in order to describe the formation of large-scale structures. On the other hand, the so-called “separate-universe” approach aims to provide an effective description of cosmological perturbations at large scales. In this talk, we will formulate the perturbation theory and the separate universe approach in the Hamiltonian language. We will then compare both frameworks to determine the domain of validity of the separate universe. As expected, both match at large scales since anisotropic degrees of freedom decouple from homogeneous ones. We’ll finish discussing the gauge matching between both approaches and the construction of their gauge-invariant quantities.