Searching for Secluded Dark Matter via Direct Detection of Recoiling Nuclei as well as Low Energy Electrons

TL;DR

This work analyzes secluded dark matter models in which a light mediator X connects a TeV-scale WIMP to Standard Model leptons, motivated by cosmic-ray anomalies. It develops a unified propagator-based framework for three model classes—Model I (kinetic mixing), Model II (mass mixing/Stueckelberg), and Model III (direct coupling)—and derives direct-detection predictions for both conventional nuclear recoils and unconventional electron recoils. In the massless-mediator limit, electron-recoil rates can be substantial with distinctive time modulation, potentially observable with sub-keV or even single-electron sensitive detectors; in the massive-mediator case, rates approach standard CDM expectations but remain sensitive to model parameters. The authors propose experimental concepts like a spherical proportional counter to detect ultra-low-energy electrons (around 10 eV) and estimate achievable event rates, highlighting the complementary role of electron recoils in probing secluded DM scenarios and the potential to connect to the observed cosmic-ray electron–positron excesses.

Abstract

Motivated by recent cosmic ray experimental results there has been a proposition for a scenario where a secluded dark matter particle annihilates, primarily, into Standard Model leptons through a low mass mediator particle. We consider several varieties of this scenario depending on the type of mixing among gauge bosons and we study the implications in novel direct dark matter experiments for detecting low energy recoiling electrons. We find significant event rates and time modulation effects, especially in the case where the mediator is massless, that may be complementary to those from recoiling nuclei.

Figures (8)

• Figure 1: Diagramatic form of Feynman propagator appeared in eq. (\ref{['prop']}) between gauge boson "flavours" $i$ and $j$. For explicit expressions in model I see Eqs.(\ref{['gg']})-(\ref{['ZZ']}); for model II see eq. (\ref{['eff2']}).
• Figure 2: A Feynman diagram leading to the direct interaction of the WIMP $\chi$ to the quarks relevant for direct detection of dark matter. The process is mediated by the physical photon. The cross indicates merely that the exotic gauge boson has a small admixture of the photon. Similarly the WIMP can also couple to electrons.
• Figure 3: The total rates for traditional WIMP searches assuming a nucleon cross section $\sigma_N=10^{-43}$$\mathrm{cm}^{2}$ in (a). The case of the photon mediated process considered in this work is exhibited in (b). Both refer to the case of a heavy target (A=131) and were computed assuming an energy threshold of 5 KeV. The results for the Iodine target used by the DAMA experiment are almost identical.
• Figure 4: The same as in Fig. \ref{['fig:Totrate_131']} in the case of the light target $^{19}F$.
• Figure 5: The quantity $R(E_\mathrm{th})/R(\left(E_\mathrm{th} \right)_{min}$, i.e. the ratio of the event rate at a given threshold divided by that at the lowest threshold considered, as a function of the threshold energy. In (a) as predicted by traditional mechanisms (lowest threshold assumed zero). In (b) as predicted by the present model (now due to the need for a cut off the lowest threshold energy employed was 5 keV). The thick line, short dash, long dash, fine line and long short dash correspond to WIMP masses 10, 50, 100, 200 and 500 GeV respectively.