Fuzzy Dark Matter Dynamics and the Quasiparticle Hypothesis

Abstract

Dark matter may be composed of ultra-light bosons whose de Broglie wavelength in galaxies is of order 1 kpc. The standard model for this fuzzy dark matter (FDM) is a complex scalar field that obeys the Schr\"odinger-Poisson equations. The wavelike nature of FDM leads to fluctuations in the gravitational field that can pump energy into the stellar components of a galaxy. Heuristic arguments and theoretical analyses suggest that these fluctuations can be modelled by replacing FDM with a system of quasiparticles (QPs). We test this hypothesis by comparing self-consistent simulations of a Schr\"odinger field with those using a system of QPs in one spatial dimension. Simulations of pure FDM systems allow us to derive a phenomenological relation between the number of QPs that is required to model FDM with a given de Broglie wavelength. We also simulate systems of FDM and stars and find that the FDM pumps energy into the stars whether it is described by QPs or a Schr\"odinger field with the FDM adiabatically contracting and the stellar system adiabatically expanding. However, we find that QPs overestimate dynamical heating.