I will show a general gauge invariant formalism for defining cosmological averages that are relevant for observations based on light-like signals. Such averages involve either null hypersurfaces corresponding to a family of past light-cones or compact surfaces given by their intersection with timelike hypersurfaces. Afterwards, using such formalism, together with adapted "geodesic light-cone" coordinates, I will show as backreaction effect emerges in the evaluation of observables related to the luminosity distance-redshift relation in an inhomogeneous Universe. To conclude, considering a realistic stochastic spectrum of inhomogeneities of primordial (inflationary) origin, I will show the magnitude and behaviour of such backreaction effects.
Address
Département de Physique Théorique
Université de Genève
24, quai Ernest Ansermet
1211 Genève 4
Switzerland
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