Parametrizing the local dark matter speed distribution: A detailed analysis

Abstract

In a recent paper, a new parametrization for the dark matter (DM) speed distribution f (v) was proposed for use in the analysis of data from direct detection experiments. This parametrization involves expressing the logarithm of the speed distribution as a polynomial in the speed v. We present here a more detailed analysis of the properties of this parametrization. We show that the method leads to statistically unbiased mass reconstructions and exact coverage of credible intervals. The method performs well over a wide range of DM masses, even when finite energy resolution and backgrounds are taken into account. We also show how to select the appropriate number of basis functions for the parametrization. Finally, we look at how the speed distribution itself can be reconstructed, and how the method can be used to determine if the data are consistent with some test distribution. In summary, we show that this parametrization performs consistently well over a wide range of input parameters and over large numbers of statistical ensembles and can therefore reliably be used to reconstruct both the DM mass and speed distribution from direct detection data.

A review of the discovery reach of directional Dark Matter detection

“…It concerns the properties of both the WIMP particle (mass and cross section) and the Galactic Dark Matter halo (three dimensional local WIMP velocity distribution and density). This topic may also be dealt with via either indirect detection [193] and direct detection separately [137,[193][194][195][196][197][198][199], or within a combined analysis [200,201] or in combination with collider data [202] or with the measurements of halo star kinematics [203]. However, directional detection offers a unique opportunity to constrain Dark Matter properties (particle and halo) with the results of a single experiment, thanks to the measurement of the double-differential spectrum d 2 R/dE r dΩ r .…”

Dark matter astrophysical uncertainties and the neutrino floor

“…Nevertheless it is well known from simulations that the SHM is not a good description of a Milky Waylike halo. There have been numerous attempts to find empirical fitting functions to better capture the phase space structure found in N-body and hydrodynamic simulations [26,[67][68][69][70][71] as well as parameterisations that decompose the speed or velocity distribution in an astrophysics independent way [72,73]. Some studies of data from hydrodynamic simulations suggest that the standard halo model is a satisfactory approximation to the Milky Way once baryons are taken into account (e.g., Ref.…”

Statistical issues in astrophysical searches for particle dark matter

“…The standard model for the galactic halo can be modified in non-trivial ways for the presence of a disk coinciding with the stellar disk or by the presence of tidal debris or streams reminiscent of interactions of Milky Way satellite. The challenge in this case is to find a proper parameterization of the speed distribution, for example in terms of a Chebyshev or Legendre polynomal expansion [52,53]. The number of basis function in this expansion is optimized using a Bayesian Information Criterion (BIC) = 2N p ln(N m ) − lnL max [54], where N p is the number of free parameters and N m is the number of measured points.…”