Fellow 2019-20

Julia "Jessie" Shelton


Tracking the Gravitational Footprints of Decoupled Dark Sectors

An unknown, “dark” form of matter makes up a quarter of the energy in the present-day universe, five times more than the total contribution of everything made out of ordinary matter, and behaves gravitationally like a massive particle that does not interact with the forces that hold ordinary matter together. While the Standard Model of particle physics has been resoundingly successful at explaining the results of terrestrial experiments, it notoriously lacks any particle that could possibly account for this mysterious matter. Dark matter and the dynamics that produced it in the early universe are thus one of the biggest outstanding puzzles in particle physics.

Dark matter may easily and generically have its main interactions in the early universe with other related dark particles, now long gone from the present-day universe. In this case, when dark matter is part of a bigger dark sector thermally decoupled from ordinary matter, terrestrial experiments searching for dark matter will come up empty-handed. To deduce the particle physics of dark matter, it then becomes necessary to look to the cosmos to observe the gravitational imprint of dark sectors, beyond that of dark matter itself. Professor Shelton’s proposed research will establish the gravitational footprints of a dark thermal plasma present in the hot and dense early universe. Such a plasma is a generic feature of self-interacting dark sectors, and thus these studies will apply to a broad and general class of dark matter theories, significantly advancing prospects for unraveling dark particle physics using its subtle gravitational footprints in the sky.