Astrophysics

In this talk, I will review the main ideas underlying stochastic inflation, by introducing the formalism in two independent ways. First I will start from the intuitive picture stemming from the equations of motion of the system. I will then introduce a more rigorous approach based on the in-in formalism, and show how the usual set of Langevin equations can emerge from a path integral formulation. With this understanding, I will then formulate a new, recursive method which allows to solve consistently both in slow-roll parameters and in quantum corrections. I will then discuss examples of how this method can be applied to derive corrected predictions for cosmological observables in the case of hybrid inflation, multi-field inflation, and inflation on modulated potentials.

We propose a new way to search for (hidden) cool molecular hydrogen H2 in the Galaxy through diffractive and refractive effects: Stars twinkle because their light crosses the atmosphere. The same phenomenon is expected on a longer time scale when the light of a remote star crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. Our simulations and test observations show that in favorable cases, the light of a background star can be subject to stochastic fluctuations on the order of a few percent at a characteristic time scale of a few minutes.

We  searched for scintillation caused by molecular gas within visible dark nebulae as well as by hypothetical halo clumpuscules of cool molecular hydrogen (H2-He) with the ESO-NTT telescope. Within a few thousands of densely sampled light-curves, we found one candidate that shows variabilities compatible with a strong scintillation effect through a turbulent structure of the B68 nebula. Furthermore, since no candidate has been found toward the SMC, we were also able to establish upper limits on the contribution of gas clumpuscules to the Galactic halo mass.

I will discuss the perspectives of synchronized observations with two large distant telescopes, to observe the time decorrelation between the light curves, an undisputable signature of the scintillation process. I will then show that a few nights of observation using the so-called « movie-mode » of LSST should allow one to significantly constrain the last unknown baryonic contribution to the Galactic mass.

Forthcoming 21cm intensity mapping surveys on the Square Kilometre Array (SKA) will be capable of probing unprecedentedly large volumes of the Universe. This will make it possible to detect effects beyond the matter-radiation equality peak in the power spectrum, including primordial non-Gaussianity, GR corrections, and possible signatures of modified gravity. I give an overview of the proposed SKA intensity mapping surveys, the science that they will be able to do, and some of the challenges that they face.