Form Factor Dark Matter

TL;DR

This work proposes a dynamical form-factor mechanism to reconcile DAMA's annual modulation with null results from other direct-detection experiments, using momentum-dependent DM–nucleus interactions generated by interference among GeV-scale gauge bosons. The authors develop two- and three-gauge-boson models that yield low-q form factors F_DM(q^2) with nodes, producing suppressed event rates outside DAMA's momentum window, and analyze their viability under standard and Via Lactea halo velocity distributions. They show that the standard halo model severely constrains such a form-factor explanation, while Via Lactea-inspired halos VL_220 and VL_270 reopen substantial regions of parameter space, particularly for the three-gauge-boson model, yielding DAMA-compatible spectra with manageable null results. The study outlines clear experimental predictions and signatures to distinguish this scenario from inelastic dark matter, emphasizing the role of halo modeling and future direct-detection data, as well as potential collider and channeling probes. Overall, form-factor dark matter provides a concrete, testable alternative to iDM for explaining DAMA while remaining consistent with other constraints under certain astrophysical assumptions.

Abstract

We present a dynamical alternative to inelastic dark matter as a way of reconciling the modulating signal seen at DAMA with null results at other direct detection experiments. The essential ingredient is a new form factor which introduces momentum dependence in the interaction of dark matter with nuclei. The role of the form factor is to suppress events at low momentum transfer. We find that a form factor approach is most likely not viable in the context of the standard halo model, however it is consistent with halo models suggested by recent Via Lactea simulations. As an example of possible form factors, we present a class of models where the necessary momentum dependence arises from interference of GeV mass gauge bosons coupling the dark matter to nuclei. At energies relevant for direct detection experiments these models contain one or two additional parameters beyond the case of a standard WIMP.

Figures (7)

• Figure 1: Overlap in $q$ of the DAMA signal with several null experiments. The height of the null experiments has no particular meaning.
• Figure 2: Schematic Feynman diagram for a form factor.
• Figure 3: An example of a spectrum from an idealized form factor. The discontinuous drop at low energies is by construction, to suppress all events outside of the DAMA signal range, while the discontinuous drop at high energies arises from the fact the escape velocity $v_{\rm esc}$ cuts off the phase space beyond that point.
• Figure 4: Constraints on idealized form factors for different halo models. For each dark matter mass, we choose a form factor to explicitly match the DAMA spectrum, as described in the text. The confidence levels at DAMA, CDMS and CRESST2 are then plotted. We use a $\chi^2$ goodness-of-fit test to define the confidence at DAMA, and the $pmax$ method for CDMS and CRESST2. The standard halo model leaves very little room for a form factor explanation for all of the data. Highlighted regions have all constraints below 95%.
• Figure 5: Exclusion plots for the two-gauge-boson (2GB) model. Confidence limits from DAMA are shown in purple (light blue) for 90% (99%), all other confidence limits are 99%. The spectrum at DAMA is shown for a benchmark point with VL$_{220}$; see table \ref{['tab:bench']} for the model parameters. $\sigma_p$ is taken in units of cm$^2$.