Cosmologie

Context. One of the main questions in modern physics concerns the origin of the Universe and the mechanisms at work in the very first moments after the Big Bang. Thanks to the considerable progress made over the past decade, largely driven by the European-led Planck satellite, the stage is set to begin to address this question formally and precisely. In this context, the most promising observational probe is the cosmic microwave background (CMB) and in particular its polarization.

The study of the cold Universe allows us to go back to the origins of our solar system by observing the embryos of stars, or to the origins of the Universe by measuring the polarisation of the Cosmic Microwave Background (CMB). These sub-millimetre and millimetre instruments require the use of superconducting detectors cooled down to 100mK. Kinetic Inductance Detectors (KIDs) are based on superconducting resonators and are about to replace bolometers thanks to their natural frequency multiplexing and ease of production (in their basic form). 

Summary

The proposed thesis aims to develop and apply a probabilistic programming language written in JAX and using SPMD parallelism on GPUs to scale Bayesian inference tasks on large cosmological datasets. This language has no equivalent on the market and will be a major asset for the scientific community. The thesis will require the development of low-level code and will be led collaboratively following the open-source philosophy.

Contexte. L'une des principales questions de la cosmologie et de la physique modernes concerne l'origine de l'Univers tel que nous le connaissons aujourd'hui. Grâce aux progrès considérables réalisés au cours de la dernière décennie, en grande partie sous l'impulsion du satellite Planck dirigé par l'Europe, le décor est planté pour commencer à aborder cette question de manière formelle et précise.

Inflation is an important theory of the primordial universe that explains amongst other things the origin of the fluctuations observed in the cosmic microwave background (CMB) and of the large-scale structure of the galaxy distribution. However, there are many different inflation models and one of the challenges of modern cosmology is to find ways to distinguish these models at the level of their predictions for observables, in order to confront them with experimental data.