Revealing hidden particles and forces with gravitational clues

Katelin Schutz
University of McGill

Abstract

How different would our Universe look with the addition of extra particles and forces beyond what we know? We already have ample gravitational evidence for at least one invisible component of matter that has properties unlike anything we have previously discovered. This dark matter is often assumed to be made of a single species of relatively inert particles but there is a much richer range of possibilities, including scenarios where dark matter is part of a “dark sector” including other auxiliary particles and forces. If there are dark forces affecting the distribution of dark matter in our Universe, then that distribution will gravitationally affect the visible matter that we can see. In this colloquium I will show how this gravitational footprint can reveal the internal properties of dark sectors where dark matter can dissipate energy, can scatter with itself (elastically or inelastically), can be wavelike on astrophysical scales, or can be born non-thermally in the moments after the Big Bang. In showing how these possibilities can be tested empirically, I will emphasize the constraining power of diverse astrophysical systems including the local Milky Way, nearby dwarf galaxies, distant galaxies and galaxy clusters, large-scale cosmological structure, and the cosmic microwave background.