Date: October 16th 2018, 2pm
Speaker: Sylvain Vanneste (LAL)
Title: Detecting CMB B-modes
The discovery of the Cosmic Microwave Background (CMB) by Penzias and Wilson in 1964 was an important confirmation of the Big Bang theory. The CMB constitutes a background of photons emitted during the first instants of our Universe history, and still permeates it today. Since its discovery, numerous telescopes, balloon-born, or satellite experiments such as Planck, have made it possible to produce measurements and precise temperature maps of the CMB, of which we have been able to deduce important information about our Universe.
However, a piece of the cosmological puzzle is still missing: the inflation, corresponding to a short period during which the Universe would have seen its size growing exponentially. Inflation is a theory introduced to solve several major cosmological questions, and which, to date, has only been verified indirectly.
The inflation phase, however, should produce a stochastic background of primordial gravitational waves that may have left an imprint on the CMB. More particularly, these gravitational waves would induce the so-called B-modes patterns on the polarisation maps of CMB photons. The precise measurement of the B-modes, still undetected to this day, represents the most powerful probe of inflationary physics.
The B-modes expected signal is however of low intensity, and many additional experimental difficulties arise when aiming at measuring it. Dust from our own galaxy partially masks the CMB, and many models are developed to clean up galactic contaminations. The extraction and analysis of the measured data signal thus requires the development of precise statistical algorithms. These must take into account the complexity of the data produced, such as residual galactic contaminations, incomplete sky map coverage, as well as statistical and instrumental errors.