Observational Constraints on Dissipative Dark Matter

Abstract

Models for dissipative, disk-forming dark matter are explored in the context of Double Disk Dark Matter. The basics of the model are reviewed. Observational constraints are placed on the parameter space of these models. The first constraint comes from the kinematics of local Milky Way stars. It is argued that most constraints in the literature only apply to the dark matter halo but not to a dark disk. Moreover it is shown that the constraints that do apply to a dark disk are mitigated by non-equilibrium features in the tracer star populations. Constraints are also placed from the distribution of Milky Way interstellar gas. Here, it is shown that a disk of dark matter may be needed to counter the effect of the gas's magnetic pressure. The possible relationship between a dark disk and the periodicity in the crater record on Earth is also revisited and a dark disk scenario is found to be strongly favored. Direct detection prospects are also explored. The density enhancement in the dark disk and the lower relative velocity are found to play a key role. The exlusion limits on the X particles from nuclear recoil are worked out, as well as ranges of sensitivity for the lighter C particles.