Cosmologie

The characterization of the polarized fluctuations of the Cosmic Microwave Background (CMB) is a major scientific way to further understand the primordial Universe. QUBIC (Q & U Bolometric Interferometer for Cosmology) is an international experiment dedicated in the measurement of this signal. It is based on a new detection technique called bolometric interferometry in order to combine the high immunity to systematic effects of an interferometer with the high sensitivity of low temperature incoherent detectors.

To optimise the optical performances of a future space instrument dedicated to CMB polarisation observations, it will be very interesting to reduce the physical size of the focal plane without decreasing the number of detectors. An elegant way to reach such architecture would be to use multichroic detectors that are sensitive to multiple frequency bands. A large bandwidth antenna could be used to feed multiple detectors (TESs or KIDs) through different bandpass filters.

L’étude des fluctuations polarisées du rayonnement fossile à 3K (Cosmic Microwave Background, CMB) apparaît aujourd’hui comme une voie incontournable pour progresser dans notre compréhension de l’Univers.

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 galaxy clusters. 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.

The Cosmic Microwave Background (CMB) radiation is a relic emission from 380 000 years after the Big-Bang. The small temperature fluctuations, resulting from quantum perturbation generated in the early Universe, contain precious information about the physics of the primordial Universe and the cosmological parameters describing in the framework of the standard cosmological model, the dynamics of the Universe and its physical content.

The goal of this thesis is to apply deep learning to the detection of galaxy clusters in astronomical surveys.  Clusters are the most massive objects in the universe, hosting hundreds of galaxies and a gaseous intra-cluster medium (ICM) at temperatures of tens of millions of Kelvin.  They are detected as galaxy over-densities in optical/near-infrared (NIR) imaging, through the X-ray emission of their ICM or via the Sunyaev-Zeldovich (SZ) effect, a distortion of the cosmic microwave background spectrum generated by photon-electron scattering in the ICM.  Clusters serve as powe

Many popular theories of the early Universe predict that gravitational waves were generated in the very first moments of its life. These theories generally invoke new physics from beyond the standard model of the particle physics and the primordial gravitational waves are believed to carry clues about the nature of those new physics laws. Detecting the primordial gravitational waves would thus have revolutionary impact on our understanding of cosmology and fundamental physics.

Many popular theories of the early Universe predict that gravitational waves were generated in the very first moments of its life. These theories generally invoke new physics from beyond the standard model of the particle physics and the primordial gravitational waves are believed to carry clues about the nature of those new physics laws. Detecting the primordial gravitational waves would thus have revolutionary impact on our understanding of cosmology and fundamental physics.

This PhD project focuses on the physics of the Cosmic Microwave Background both from an observational and from a theoretical perspective. This PhD will be co-supervised by Martin Bucher and Ken Ganga at APC in Paris. It is also envisaged that the student will take part in exchanges with  researchers at the University of Tokyo.

During the last decade, cosmology has entered a precision era, leading to the prevalence of the standard cosmological model, ΛCDM. Nevertheless the main ingredient of this model, dark energy, while dominating the energy budget of our Universe, remains mysterious and its comprehension is the current Graal of the domain.