Nuclear scattering of dark matter coupled to a new light scalar

Abstract

We consider the nuclear scattering cross section for the eXciting Dark Matter (XDM) model. In XDM, the Weakly Interacting Massive Particles (WIMPs) couple to the Standard Model only via an intermediate light scalar which mixes with the Higgs: this leads to a suppression in the nuclear scattering cross section relative to models in which the WIMPs couple to the Higgs directly. We estimate this suppression factor to be of order 10^(-5). The elastic nuclear scattering cross section for XDM can also be computed directly: we perform this computation for XDM coupled to the Higgs sector of the Standard Model and find a spin-independent cross section in the order of 4 x 10^(-13) pb in the decoupling limit, which is not within the range of any near-term direct detection experiments. However, if the XDM dark sector is instead coupled to a two-Higgs-doublet model, the spin-independent nuclear scattering cross section can be enhanced by up to four orders of magnitude for large tan(beta), which should be observable in the upcoming SuperCDMS and ton-scale xenon experiments.

Figures (4)

• Figure 1: t-channel WIMP-nucleus scattering via Higgs transfer.
• Figure 2: t-channel WIMP-nucleus scattering via $\phi$-mediated Higgs transfer (XDM scenario).
• Figure 3: Variation of the cross section with $\tan \beta$ for XDM coupled to a two-Higgs-doublet model, for $m_A = 300, 400, 500$ GeV. The thick lines correspond to cases where the light Higgs mass is held constant at $100$ GeV, whereas the thin lines use the tree-level MSSM values.
• Figure 4: Current experimental limits and theoretical predictions for the spin-independent proton-WIMP elastic scattering cross section. The lower dashed line is the estimated cross section for XDM coupled to the Standard Model, calculated in this paper. The upper dashed line is the cross section for XDM coupled to a 2HDM with $\tan \beta = 50$ and $m_A = 300$ GeV, as shown in Fig. \ref{['twohiggsfig']}.