Gauge invariant averages in cosmology: from spatial to null hypersurfaces

Repeats every 2 days until Fri Feb 01 2013 .
Mon, 28/01/2013 - 11:00 - 13:00
Wed, 30/01/2013 - 11:00 - 13:00
Fri, 01/02/2013 - 11:00 - 13:00
Giovanni Marozzi

The Universe on large scale turns out to be well described by a homogeneous and isotropic FLRW space-time plus perturbations. On the other hand, one of the most lively field in cosmology is the study of the level to which such perturbation influence the cosmological observable and the dynamics of the Universe, at least at an averaged level. After a short resume of the so-called cosmological perturbation theory and of the relative gauge problem, I will introduce a general gauge invariant formalism that allow us to define physical observers and the relative spatial averages (generalizing the standard Buchert approach). Such gauge invariant formalism to average over spacelike hypersurfaces will be then used to succeed in the definition of a prescription to average over null hypersurfaces, prescription useful to investigate observations based on light-like signals. To conclude, I will define an adapted coordinate system over light-cone hypersurfaces and the relative perturbation theory.