Cosmology seminar - Andrew Eberhardt

Given our current understanding of the universe, about a fourth of the cosmic energy density must be "dark" matter. And while the abundance and interaction strength are well constrained, the particle nature is entirely unknown. A global effort combines simulations, observation, and theory to search approximately 100 orders of magnitude of mass parameter space in an attempt to identify the dark matter particle. At the lowest mass end, around 1e-19 eV and below, the particle is so light that it manifests quantum effects on galactic scales. In this regime, simulations of structure formation provide some of the strongest constraints on the dark matter mass. These simulations use the classical field approximation to make numerical results computationally feasible. Recently, there has been debate in the community as to whether this approximation is sufficient to describe the behavior of ultra light dark matter on all length and time scales relevant to current constraints. We critically examine this claim by developing some of the largest and most accurate quantum field simulations of ultra light dark matter. Our work identifies the scales on which this approximation breaks down and the effect of quantum corrections. We find that corrections grow exponentially and impact the density profile predictions of this model.