Campus, Varian 355

The universe has gone through two phases of accelerated expansion: a primordial phase called cosmic inflation and an ongoing phase that has been taking place for the last 6 billions years.

To explore cosmic inflation, we are now on the hunt for the primordial cosmic microwave background (CMB) B-modes. This signal is expected to be tenuous so we need to characterize and understand the different sources of CMB B-modes beyond cosmic inflation. In the first part of this talk, I will highlight results from Lemarchand et al, submitted to A&A, 2018 (arXiv:1810.09221 <https://arxiv.org/abs/1810.09221> ) and my ongoing work addressing one astrophysical effect: Faraday rotation from magnetic field in clusters. I will explain this phenomenon and show results of its impact on CMB B-modes.

In the second part of my talk I will focus on understanding the origin of the ongoing cosmic acceleration. Observations are indeed showing that the universe is currently going through a phase of accelerated expansion. Different explanations for this acceleration are possible. One possiblity is that general relativity does not correctly describe the laws of gravity on cosmological scales. I have been interested in doing tests of gravity using cosmological observables of the growth of structure and especially weak gravitational lensing. I will first give a general introduction to the problem of cosmic acceleration and its observables. I will then present the results from Ferté et al, to appear in PRD (arXiv:1712.01846 <https://arxiv.org/abs/1712.01846> ) constraining deviations to general relativity using available data sets, in addition to forecasts of these constraints with future experiments. I will end presenting a similar analysis and results I have been involved in using the first year of observation of the Dark Energy Survey (DES collaboration, submitted to PRD, 2018 arXiv:1810.02499 <https://arxiv.org/abs/1810.02499> ). I will also highlight constrains on extensions to the standard model of cosmology from this work.