CMB B-mode studies are amongst some of the most exciting, contemporary endeavors in the field of cosmology. They are broadly expected to provide a new, unique window on the physics of the very early Universe, potentially detecting primordial gravitational waves, giving a very strong evidence in favor of inflation as a correct paradigm, within which to model this phase of the Universe's evolution, and thus potentially constraining some of the fundamental energy scales of physics. These are hoped to provide some essential clues for high energy physics models.
In addition, thanks to the fact that some of the observed B-mode is converted from the E-mode signal due to the gravitational lensing of the CMB photons by the growing large scale structures, it could set unique complementary constraints on dark energy properties at the redshift z around 1-2 and on the masses of the neutrinos, with a precision surpassing the one expected of future laboratory experiments by a factor of at least 10 and sufficient to resolve the neutrino mass hierarchy problem.
Two ingredients are necessary to achieve these fascinating objectives: a powerful data set and robust data analysis techniques. Development of the latter and their application to the actual data sets is the focus of work of our group at APC. The access to some of the most advanced and exciting data sets is ensured by our involvement in the POLARBEAR/Simons Array (PB/SA) experiment. This is one of the leading, currently operating CMB observatories, which conducts the observations from the Atacama desert in Chile. The observatory will be soon equipped with three independent telescopes, observing the sky in multiple frequency bands with more than 20,000 highly sensitive detectors. The experiment is expected to continue providing new data continuously until 2019, effectively producing one of the richest and most exciting data sets of this kind available on this time scale. We are also involved in the preparation and design of the future efforts, in particular the next-generation of ground based experiments, Simons Observatory and CMB-S4, as well as satellite missions, e.g., JAXA/NASA LiteBIRD.
The goal of the PhD project proposed here is an analysis and scientific exploitation of the PB/SA data sets separately and in combination with other cosmological data. The specific target of the work will be the development of techniques for a robust power spectrum estimation and cosmological parameter estimation with the goals of setting limits on both the energy scale of inflation and masses of neutrinos.
The work will involve devising and implementing algorithms relevant to such tasks, validating them on simulated data, and later applying them as part of the end-to-end data analysis pipeline to the real data sets. The student will also have an opportunity to take part in the observational campaigns conducted from Chile.
This PhD project will be performed as part of the work of a broader European collaboration, involving former POLARBEAR students at APC and other researchers. This provides a closely knit, friendly and efficient environment to start and conduct this kind of research within. The work will also involve a number of remote collaborations with teams in Berkeley (University of California, Berkeley) and Japan (KEK, Tsukuba; IPMU Tokyo) as well as potential extended visits in both the US and Japan.
Modern cosmological data analysis is an interdisciplinary endeavor, involving elements of physics, numerical methods, statistics, and applied mathematics, amounting to a new mode of scientific research. Its importance has been steadily increasing, reflecting the transformation of cosmology from a data-starved to a data-driven science. Our group at APC is involved in a number of dynamic, interdisciplinary collaborations including statisticans, computer scientists and applied mathematicians aiming at addressing problems faced by the CMB data analysis in novel original ways. This PhD thesis is therefore expected to help the candidate developing diverse skills eagerly sought-after in scientific and other societal contexts.
This project could be preceded by an M2 internship (see M2 project "Impact of foregrounds on search for primordial gravitational waves with current and planned CMB observations" proposed by R. Stompor and J. Errard (APC)).