SHM${}^{++}$: A Refinement of the Standard Halo Model for Dark Matter Searches in Light of the Gaia Sausage

Abstract

Predicting signals in experiments to directly detect dark matter (DM) requires a form for the local DM velocity distribution. Hitherto, the standard halo model (SHM), in which velocities are isotropic and follow a truncated Gaussian law, has performed this job. New data, however, suggest that a substantial fraction of our stellar halo lies in a strongly radially anisotropic population, the 'Gaia Sausage'. Inspired by this recent discovery, we introduce an updated DM halo model, the SHM${}^{++}$, which includes a `Sausage' component, thus better describing the known features of our galaxy. The SHM${}^{++}$ is a simple analytic model with five parameters: the circular speed, local escape speed and local DM density, which we update to be consistent with the latest data, and two new parameters: the anisotropy and the density of DM in the Sausage. The impact of the SHM${}^{++}$ on signal models for WIMPs and axions is rather modest since the multiple changes and updates have competing effects. The largest change occurs for directional detectors which have sensitivity to the full three-dimensional velocity distribution.

arXiv commentPRD, in press. This version updates the discussion on the escape speed

References in corpus (1)

• First results from the HAYSTAC axion search

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• Uncertainties in Direct Dark Matter Detection in Light of Gaia's Escape Velocity Measurements
• On the correlation between the local dark matter and stellar velocities
• Towards a more rigorous treatment of uncertainties on the velocity distribution of dark matter particles for capture in stars