Spin-Dependent WIMPs in DAMA?

TL;DR

The paper investigates whether DAMA's annual modulation can arise from spin-dependent WIMPs with axial-vector couplings. Using a model-independent analysis, it maps the DAMA-favored regions into $(M_\chi, \sigma^{SD}_{\chi p})$ and $(M_\chi, \sigma^{SD}_{\chi n})$ planes and tests them against external constraints, including solar-neutrino flux limits and xenon-based detectors, while employing the rate formalism with SD and SI form factors and a $\kappa$-based compatibility metric. The main findings are that SD WIMP-proton scenarios are excluded by upper limits on neutrino-induced muons from the Sun, and SD WIMP-neutron scenarios are excluded for $M_\chi \gtrsim 20$ GeV by Xe data, leaving only a small, low-mass region ($M_\chi \lesssim 20$ GeV) requiring an extreme $a_n/a_p$ ratio (about four orders of magnitude). These results significantly constrain SD explanations for the DAMA modulation and emphasize the power of multi-channel astrophysical and terrestrial constraints in dark-matter phenomenology.

Abstract

We investigate whether the annual modulation observed in the DAMA experiment can be due to a weakly-interacting massive particle (WIMP) with an axial-vector (spin-dependent; SD) coupling to nuclei. We evaluate the SD WIMP-proton cross section under the assumption that such scattering accounts for the DAMA modulation, and we do the same for a SD WIMP-neutron cross section. We show that SD WIMP-proton scattering is ruled out in a model-independent fashion by null searches for energetic neutrinos from WIMP annihilation in the Sun, and that SD WIMP-neutron scattering is ruled out for WIMP masses > 20 GeV by the null result with the DAMA Xe detector. A SD WIMP with mass < 20 GeV is still compatible, but only if the SD WIMP-neutron interaction is four orders of magnitude greater than the WIMP-proton interaction.

Figures (2)

• Figure 1: The shaded region shows the parameter space (in WIMP mass versus SD WIMP-proton cross section) implied by the Dama annual modulation for a WIMP with exclusively SD interactions with protons and no interaction with neutrons. The solid curve indicates the upper bound to the SD WIMP-proton cross section from null searches for neutrino-induced upward muons from the Sun; thus the cross hatched region is excluded.
• Figure 2: The shaded region shows the parameter space (in WIMP mass versus SD WIMP-neutron cross section) implied by the Dama annual modulation under the assumption that the signal is due exclusively to SD WIMP-neutron scattering. The solid curve indicates the upper bound to the SD WIMP-neutron cross section from the Dama Xe detector. Again the cross hatched region is excluded.