Non-parametric uncertainties in the dark matter velocity distribution

Abstract

We investigate the impact of uncertainty in the velocity distribution of dark matter on direct detection experiments. We construct an multinomial prior with a hyperparameter $\beta$ that describes the strength of our belief in an isotropic Maxwell-Boltzmann velocity distribution. By varying $\beta$, we interpolate between a halo-independent and halo-dependent analysis. We present a novel approximation for the marginalisation of this prior that is applicable to any counting experiment. With this formula, we investigate the impact of the uncertainty in limits from XENON1T. For dark matter masses greater than about 60 GeV, we find extremely mild sensitivity to the distribution. Below about 60 GeV, the limit weakens by less than an order of magnitude if we assume an isotropic distribution in the galactic frame. If we permit anisotropic distributions, the limit further weakens, but at most by about two orders of magnitude. Lastly, we check the impact of parametric uncertainties and discuss the possible inclusion and impact of our technique in global fits.

arXiv commentto appear in JCAP. Numerical results unchanged, but moderate changes to presentation and interpretation of formalism

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• Dark matter capture by the Sun: revisiting velocity distribution uncertainties
• Direct Detection Anomalies in light of $Gaia$ Data
• Uncertainties on the EFT coupling limits for direct dark matter detection experiments stemming from uncertainties of target properties
• Constraints on dark matter interactions from the first results of DarkSide-50
• Precise interpretations of traditional fine-tuning measures
• Information divergences to parametrize astrophysical uncertainties in dark matter direct detection
• Information-theoretic astrophysical uncertainties in the effective theory of dark matter direct detection