Dark matter local density determination: recent observations and future prospects

Abstract

This report summarises progress made in estimating the local density of dark matter ($\rho_{\mathrm{DM,\odot}}$), a quantity that is especially important for dark matter direct detection experiments. We outline and compare the most common methods to estimate $\rho_{\mathrm{DM,\odot}}$ and the results from recent studies, including those that have benefited from the observations of the ESA/Gaia satellite. The result of most local analyses coincide within a range of $\rho_{\mathrm{DM,\odot}} \simeq \text{0.4--0.6}\,\mathrm{GeV/cm^3} = \text{0.011--0.016}\,\mathrm{M_\odot / pc^3}$, while a slightly lower range of $\rho_{\mathrm{DM,\odot}} \simeq \text{0.3--0.5}\,\mathrm{GeV/cm^3} = \text{0.008--0.013}\,\mathrm{M_\odot / pc^3}$ is preferred by most global studies. In light of recent discoveries, we discuss the importance of going beyond the approximations of what we define as the Ideal Galaxy (a steady-state Galaxy with axisymmetric shape and a mirror symmetry across the mid-plane) in order to improve the precision of $\rho_{\mathrm{DM,\odot}}$ measurements. In particular, we review the growing evidence for local disequilibrium and broken symmetries in the present configuration of the Milky Way, as well as uncertainties associated with the Galactic distribution of baryons. Finally, we comment on new ideas that have been proposed to further constrain the value of $\rho_{\mathrm{DM,\odot}}$, most of which would benefit from Gaia's final data release.