Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons

TL;DR

This study uses a high-resolution cosmological simulation including baryons to analyze the local dark matter phase-space structure and its impact on direct detection signals, revealing a dark disk and non-Gaussian velocity distributions that affect experimental interpretations.

Contribution

It provides the first detailed analysis of how baryonic effects and non-standard velocity distributions influence dark matter direct detection signals, especially regarding the DAMA modulation.

Findings

Dark disk contributes ~25% to local DM density.

Velocity distributions deviate from Maxwellian, affecting detection predictions.

Compatibility between DAMA and other experiments improves with non-Maxwellian models.

Abstract

We extract at redshift z=0 a Milky Way sized object including gas, stars and dark matter (DM) from a recent, high-resolution cosmological N-body simulation with baryons. Its resolution is sufficient to witness the formation of a rotating disk and bulge at the center of the halo potential. The phase-space structure of the central galactic halo reveals the presence of a dark disk component, that is co-rotating with the stellar disk. At the Earth's location, it contributes to around 25% of the total DM local density, whose value is rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations from pure Gaussian and Maxwellian distributions, with a sharper drop of the high velocity tail. We give a detailed study of the impact of these features on the predictions for DM signals in direct detection experiments. In particular, the question of whether the modulation signal observed by DAMA is or is not excluded by limits set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and compared to the case of a standard Maxwellian halo, in both the elastic and the inelastic scattering scenarios. We find that the compatibility between DAMA and the other experiments is improved. In the elastic scenario, the DAMA modulation signal is slightly enhanced in the so-called channeling region, as a result of several effects. For the inelastic scenario, the improvement of the fit is mainly attributable to the departure from a Maxwellian distribution at high velocity.