Speaker
Description
With high-precision data about to be delivered by large-scale surveys, the development of higher-order perturbative descriptions of cosmological observables is becoming increasingly important. Among the others, the redshift drift, being sensitive to local variations in the Hubble factor, paves the way for direct tests of the cosmic acceleration history. More in general, it enables real-time cosmology, which aims to determine the redshift evolution of observables measured on the past light-cone of an observer.
The Geodesic Light-Cone coordinates provide a natural framework for this purpose, as they are specifically adapted to the observer’s past light-cone and allow for a non-perturbative description of light propagation in an inhomogeneous Universe.
In this talk, I will first review how these coordinates are defined. I will then describe a cosmological perturbation theory constructed directly on the observed past light-cone up to second order, using a fully gauge-invariant approach. This framework enables the consistent computation of higher-order corrections to cosmological observables in General Relativity as well as in modified gravity and dark energy scenarios.
I will focus on non-linear relativistic effects on the redshift drift, by combining analytical and numerical results and discussing about their validity also for cosmological models beyond LambdaCDM. In particular, I will demonstrate that, unlike widely studied observables such as the galaxy number counts, the bispectrum of the redshift drift is inherently more sensitive to non-linear effects than its two-point statistics.
[Based on JCAP 03 (2026) 075 and arXiv:2604.26690]