Revisiting the escape speed impact on dark matter direct detection

The knowledge of the high velocity tail of the WIMP (Weakly Interacting Massive Particles)
velocity distribution has a strong impact on the way dark matter direct detection (DMDD) may
constrain or discover light WIMPs in the GeV mass range. Recently, there have been important
observational efforts to estimate the Galactic escape speed at the position of the Earth, like for instance
the analysis published in early 2014 by the RAVE Collaboration (Piffl et al., 2014), which is
of interest in the perspective of reducing the astrophysical uncertainties in DMDD. Nevertheless,
these new estimates cannot be used blindly as they rely on assumptions on the Milky Way mass
distribution, which induce tight correlations between the escape speed and other local astrophysical
parameters (circular speed and dark matter density). We make a self-consistent study of the
implications of the RAVE results on DMDD assuming isotropic DM velocity distributions, both
Maxwellian and ergodic. Taking as reference the experimental sensitivities currently achieved
by LUX, CRESST2, and SuperCDMS, we show that the uncertainties inferred for the exclusion
curves in the low WIMP mass region are moderate, ranging from 10% to 20% , and that
the RAVE results imply large values of r , and so correspond to exclusion curves that are more
constraining than the standard ones by 40%.