Lightcone Averaging and Precision Cosmology

Understand

The first objective of this thesis is to fill the lack in cosmology of a description on the past light cone: the null hypersurface on which observed signals propagate.

• Its second goal is to evaluate the importance of inhomogeneities in the determination of dark energy parameters, whose real nature is still unknown and for which the influence of matter structures has been proposed as a cosmological alternative.
• We start with the definition of a "geodesic lightcone" gauge simplifying greatly the study of light propagation in the Universe.
• We then define a gauge invariant average of scalars on the past light cone and compute the effect of inhomogeneities on the luminosity flux by considering their power spectrum up to its non-linear regime.