On the Origin of Light Dark Matter Species

TL;DR

The paper proposes a GeV-scale supersymmetric dark sector in which stable GeV-Matter, such as dark higgsinos, interacts with the Standard Model via a kinetically mixed U(1)_D. A fixed proton-cross-section makes even a small GeV-Matter abundance observable in direct-detection experiments, and two production paths are explored: thermal freeze-out and late decay of a TeV-scale WIMP. The authors demonstrate that inelastic down-scattering with keV-scale splittings can reconcile CoGeNT and DAMA data while remaining compatible with XENON10 and CDMS-Si uncertainties, and they outline concrete B-factory tests and UV completions. The framework also offers a coherent link to cosmic-ray anomalies through decays of heavy WIMPs, predicting rich, testable signatures across low-energy experiments and colliders. Overall, the work presents a predictive, testable scenario where a GeV-scale dark sector plays a central role in explaining multiple astrophysical and terrestrial signals.

Abstract

TeV-mass dark matter charged under a new GeV-scale gauge force can explain electronic cosmic-ray anomalies. We propose that the CoGeNT and DAMA direct detection experiments are observing scattering of light stable states -- "GeV-Matter" -- that are charged under this force and constitute a small fraction of the dark matter halo. Dark higgsinos in a supersymmetric dark sector are natural candidates for GeV-Matter that scatter off protons with a universal cross-section of 5 x 10^{-38} cm^2 and can naturally be split by 10-30 keV so that their dominant interaction with protons is down-scattering. As an example, down-scattering of an O(5) GeV dark higgsino can simultaneously explain the spectra observed by both CoGeNT and DAMA. The event rates in these experiments correspond to a GeV-Matter abundance of 0.2-1% of the halo mass density. This abundance can arise directly from thermal freeze-out at weak coupling, or from the late decay of an unstable TeV-scale WIMP. Our proposal can be tested by searches for exotics in the BaBar and Belle datasets.

Figures (4)

• Figure 1: Left: Regions of scattering cross-section per nucleon times GeV-Matter mass fraction in the halo versus mass favored by CoGeNT (filled regions), DAMA with channeling (solid-line contours), and DAMA without channeling (dashed contours) for light dark matter scattering coherently off protons. We show favored regions (from right to left) for elastic scattering (green) and inelastic splittings $|\delta|=15$ keV (orange), $25$ keV (red), and $35$ keV (blue), with equal fractions of up- and down-scattering. The contours correspond to "$1.6\sigma$," neglecting systematic uncertainties. The black dot and upside-down triangle correspond to benchmark points we consider in Figure \ref{['fig:DAMACogentfit']}. Right: A close-up of the $|\delta|=25$ keV allowed region with "$3\sigma$" contours added and constraints from XENON10 (black lines) and CDMS-Si (gray lines). Thick (thin) lines denote 5.0 (2.3) events expected, again neglecting systematics. More details are given in §\ref{['sec:DirectDetection']}.
• Figure 2: A fit (solid red line) to the CoGeNT data (left) and DAMA data (right). In the CoGeNT fit, we assume an energy-dependent detection efficiency Aalseth:2010vx and include four contributions: dark matter (red dashed), two gaussians for the cosmogenic peaks near 1.1 keV and 1.29 keV (green and blue dashed), and a constant background (gray dashed). The dark matter mass (5.0 GeV), cross-section ($1.4\times 10^{-40}$ cm$^2$), and splitting $\delta=25$ keV correspond to a benchmark point that fits both data sets very well (indicated by the dot in Figure \ref{['fig:DD1']}). The expected number of events in CDMS-Si and XENON10 is about 4.3 and 0, respectively. Assuming a 20% larger energy threshold in CDMS-Si would lead to 1.1 events expected.
• Figure 3: The effect of energy thresholds on XENON10 and CDMS-Si Limits. Left: The contours and thin solid lines are as in the left panel of Figure \ref{['fig:DD1']}. The dashed black and gray lines indicate the change in XENON10 and CDMS-Si sensitivity when their threshold energy is increased by 20%. In the case of CDMS-Si, we use the same rescaling of recoil energies in determining the detection efficiency. Right: The spectra in CDMS-Si for the benchmark point with $\delta=25 \,\mathrm{keV}$ (top panels of Figure \ref{['fig:DAMACogentfit']}), assuming the nominal efficiency (blue solid curve) or assuming a 20% offset of the energy threshold and energy-dependent efficiency (dashed green curve). The total scatter rate with no efficiency correction applied (thin dashed gray curve) is also shown for reference.
• Figure 4: Constraints derived from the $e^+e^-\rightarrow A' \gamma$ process in the $\mu^+\mu^-\gamma$ search in BaBar's $\Upsilon(3S)$ data using Aubert:2009cp. The gray region is excluded at more than $90\%$ confidence, while the dotted line shows the combined reach of BaBar and Belle. The blue region shows the expected range of parameters in models of light sub-dominant higgsino dark matter. While not shown, we expect that multi-lepton searches sensitive to the reaction $e^+e^-\rightarrow A' h_d$ in the four or more lepton/pion final state can reach sensitivities of order $(\epsilon c_W)^2 \sim {\cal O}(10^{-8})$:2009pw.