Abstract
Fitting the model ''A'' to dark matter direct detection data, when the model that underlies the data is ``B'', introduces a theoretical bias in the fit. We perform a quantitative study of the theoretical bias in dark matter direct detection, with a focus on assumptions regarding the dark matter interactions, and velocity distribution. We address this problem within the effective theory of isoscalar dark matter-nucleon interactions mediated by a heavy spin-1 or spin-0 particle. We analyze 24 benchmark points in the parameter space of the theory, using frequentist and Bayesian statistical methods. First, we simulate the data of future direct detection experiments assuming a momentum/velocity dependent dark matter-nucleon interaction, and an anisotropic dark matter velocity distribution. Then, we fit a constant scattering cross section, and an isotropic Maxwell-Boltzmann velocity distribution to the simulated data, thereby introducing a bias in the analysis. The best fit values of the dark matter particle mass differ from their benchmark values up to 2 standard deviations. The best fit values of the dark matter-nucleon coupling constant differ from their benchmark values up to several standard deviations. We conclude that common assumptions in dark matter direct detection are a source of potentially significant bias.
Highlights
Fitting the model “A” to dark matter direct detection data, when the model that underlies the data is “B”, introduces a theoretical bias in the fit
We address this problem within the effective theory of isoscalar dark matter-nucleon interactions mediated by a heavy spin-1 or spin-0 particle
Incorrect assumptions about the dark matter-nucleon interaction, or the local dark matter velocity distribution will bias the interpretation of future direct detection experiments
Summary
Fitting the model “A” to dark matter direct detection data, when the model that underlies the data is “B”, introduces a theoretical bias in the fit. Distribution are common assumptions in this field [24] The former assumption is motivated by the small velocity of the dark matter particles in the Milky Way, the latter by the simplicity of the Maxwell-Boltzmann distribution (i.e. a self-consistent distribution generated by the density profile of an isothermal sphere [25]). Both assumptions are wellmotivated, other interaction types and velocity distributions are plausible, and could be considered in the data analysis [26]. Interesting polynomials expansions [45], and decompositions in streams [46] to model general dark matter velocity distributions have been recently proposed
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