Speaker
Description
With high-precision data about to be released by large-scale cosmological surveys, the development of higher-order perturbative descriptions of cosmological observables is becoming increasingly important.
The so-called Geodesic Light-Cone coordinates are a physically motivated set of coordinates which account for the fact that light-rays propagate on the past light-cone of an observer. They are a powerful tool for studying the late-time universe because, trivializing light-beam propagation throughout an inhomogeneous space-time, they allow for fully non-linear expressions of light-like cosmological observables.
In this talk, I will first review how these coordinates are defined. Then, I will show how a cosmological perturbation theory up to second order can be constructed on top of a background light-cone geometry. Within this new perturbative framework and adopting a fully gauge-invariant approach, higher-order formulae for cosmological observables can be computed. I will focus on the redshift and the redshift drift. In particular, computing the non-linear general relativistic effects of the redshift drift proves that the magnitude of the three-point function is significantly larger than the naive expectation based on perturbative considerations on the two-point function. Consequently, a substantial degree of non-Gaussianity can be inferred from the bispectrum of the redshift drift. In light of future galaxy surveys observations, I will then emphasize how such a high level of non-Gaussianity could be correctly interpreted as evidence of the intrinsic non-linear nature of General Relativity.
[based on 2510.25690, astro-ph.CO and 2601.XXXXX]