Generalized spin-dependent WIMP-nucleus interactions and the DAMA modulation effect

Abstract

Abstract. Guided by non-relativistic Effective Field Theory (EFT) we classify the most general spin-dependent interactions between a fermionic Weakly Interacting Massive Particle (WIMP) and nuclei, and within this class of models we discuss the viability of an interpretation of the DAMA modulation result in terms of a signal from WIMP elastic scatterings using a halo-independent approach. We find that, although several relativistic EFT's can lead to a spin-dependent cross section, in some cases with an explicit, non-negligible dependence on the WIMP incoming velocity, three main scenarios can be singled out in the non-relativistic limit which approximately encompass them all, and that only differ by their dependence on the transferred momentum. For two of them compatibility between DAMA and other constraints is possible for a WIMP mass below 30 GeV, but only for a WIMP velocity distribution in the halo of our Galaxy which departs from a Maxwellian. This is achieved by combining a suppression of the WIMP effective coupling to neutrons (to evade constraints from xenon and germanium detectors) to an explicit quadratic or quartic dependence of the cross section on the transferred momentum (that leads to a relative enhancement of the expected rate off sodium in DAMA compared to that off fluorine in droplet detectors and bubble chambers). For larger WIMP masses the same scenarios are excluded by scatterings off iodine in COUPP.

Complete Lorentz-to-Galileo dictionary for direct dark matter detection

“…Notice that the two building blocks that can be obtained by exchanging s χ ↔ s N in O 15 and O 17 are not independent from the ones above. In fact, by using ε ijk ε iab = δ ja δ kb −δ jb δ ka to reduce (q × v ⊥ el ) · [(s 1 × s 2 ) × x] to a single cross product in two different ways, we get…”

Highlights of DAMA/LIBRA

“…in Refs. [15,21] . A further large literature is available on the topics; many possibilities are open.…”

Halo-independent determination of the unmodulated WIMP signal in DAMA: the isotropic case

“…The experiments that have by now reached a background level low enough to be sensitive to the DAMA modulation use targets different from sodium iodide. As a consequence, while for standard hypotheses on the WIMP-nucleon cross section and WIMP velocity distribution (i.e., spin-dependent or spin-independent interactions with a truncated Maxwellian distribution) the DAMA signal appears to be in strong tension with constraints from other detectors, when such assumptions are relaxed several WIMP models have been shown to exist for which the yearly modulation effect measured by DAMA can still be reconciled with the non observation of a dark matter signal in other experiments [16][17][18][19]. This shows that there is still a clear need to assess the compatibility of the DAMA excess with other detectors in a model-independent way.…”

“…Some authors define two separate velocity integralsη 0 (v min ) andη m (v min ), one for the unmodulated part S 0 and one for the modulated part S m in Eq. (1.1), and then proceed to impose either the simple inequalityη m (v min ) <η 0 (v min ) [17,18,[30][31][32][33][34][35][36][37] or more sophisticated inequalities valid for smooth distributions [24,25]. Comparing two separate velocity integrals with proper statistical significance is not straightforward.…”