Probing the Universe’s beginning and testing fundamental physics with Simons Array and Simons Observatory cosmic microwave background polarization data sets.

Context. One of the main questions of modern cosmology and physics concerns the origin of the Universe, its structure and its evolution, as we observe today. Thanks to the tremendous progress made in the last decade, in big part driven by the Europe-led satellite mission Planck, the stage has been set to start addressing this kind of questions for the first time in a meaningful way. Our most promising observational probe in this context is an observation and characterization of statistical properties of the polarization of the cosmic microwave background (CMB) - the primordial light generated at the very early Universe.
Many popular theories of the early Universe predict that gravitational waves were generated in its very first moments. These theories generally invoke new physics from beyond the standard model of particle physics, which determines properties of the primordial gravitational waves and which consequently carry clues about the nature of those new laws of physics. Detecting the primordial gravitational waves would thus have revolutionary impact on our understanding of cosmology and fundamental physics while at the same time explaining the origin of the observed structures of the Universe. CMB polarization is also expected to shed a new light on some other key questions of modern physics, such as those concerning the nature of dark matter, total mass of neutrinos and their mass hierarchy, or the presence of unknown relativistic particle species.
The telltale information is contained in a pattern of minuscule CMB polarization anisotropies, which have to be recovered from huge volumes of data collected by current and forthcoming CMB experiments, differentiate from other unwanted signals, and characterized with unprecedented precision and robustness.
The objective of the proposed thesis is to contribute to global, worldwide effort of exploiting this scientific
potential of the CMB polarization in an important and visible manner.

Thesis. The proposed thesis will be performed in the context of the two major on-going CMB experiments, Simons Array and Simons Observatory on which French researchers at APC and LAL collaborate with American and other international partners. These cutting-edge experiments will bring unprecedented volumes of data and reach sensitivity that will allow for setting tight constraints on the physical laws governing the Universe. The main objective of the thesis will be a development of new data analysis techniques suitable for the forthcoming data sets, their application to the actual data set, and participation in the exploitation of their scientific potential. While CMB polarization is one of the most exciting and active areas of modern cosmology, data analysis has matured to become one of the main pillars on which the success of this entire program is hinged.
The specific goal will be a development of novel component separation algorithms designed and optimized for the ground-based data sets, where the number of observational frequencies is limited to a few available atmospheric windows and implementing them in the presence of systematic and instrumental effects typical of ground observations. This is a key step in the CMB data analysis and a new element in the analysis of the ground CMB data with which the forthcoming experiments will have to contend. The smallness of the amplitude of the cosmological signals drives the need for necessary experimental sensitivity, what in turn sets unprecedented requirements on the control and mitigation of instrumental and environmental effects, including the so-called foreground signals generated mostly by our Galaxy. The component separation strives for separating those signals of different origins, based on their physical and statistical properties, and for producing maps of the pristine signal as produced in the early Universe. Later, the student will work on scientific exploitation of those maps and setting novel
constraints on cosmology and fundamental physics.
Modern CMB data analysis is a multi-disciplinary effort, involving statistical methods, signal processing, machine learning, high performance scientific computing in addition to physics and cosmology. The student will have an opportunity to collaborate with experts in all those fields, capitalizing on active research collaborations present already established in our laboratories. This will allow the student to develop attractive, broad scientific background and research experience well beyond that of a typical physics thesis, preparing him/her for a future career in diverse contexts. In addition, the student will have opportunity to participate hands-on in the deployment and observational campaigns.

The proposed PhD will be part of the collaborative effort between France-based researchers from the IN2P3 institute of CNRS and researchers based at the Physics Department of the University of California at Berkeley (USA) and will be performed under the auspices of a new International Research Unit (UMI), Centre Pierre Binétruy, which is currently being set up between CNRS and UC Berkeley. The student will be supervised jointly by dr. R. Stompor (CNRS/IN2P3, APC Laboratory) and prof. A. T. Lee (UCB, Physics Dept.).


R. Stompor






Email du responsable: