Direct and indirect singlet scalar dark matter detection in the lepton-specific two-Higgs-doublet model

A recent study of gamma-ray data from the Galactic center motivates the investigation of light ($\sim 7–10\mathrm{GeV}$) particle dark matter models featuring tau-lepton pairs as dominant annihilation final state. The lepton-specific two-Higgs-doublet model provides a natural framework where light, singlet scalar dark matter can pair-annihilate dominantly into tau leptons. We calculate the nucleon–dark matter cross section for singlet scalar dark matter within the lepton-specific two-Higgs-doublet model framework, and compare with recent results from direct detection experiments. We study how direct dark matter searches can be used to constrain the dark matter interpretation of gamma-ray observations, for different dominant annihilation final states. We show that models exist with the correct thermal relic abundance that could fit the claimed gamma-ray excess from the Galactic center region and have direct detection cross sections of the order of what is needed to interpret recent anomalous events reported by direct detection experiments.

Figure 1

Spin-independent DM scattering cross section off protons versus annihilation cross section times the relative velocity of the DM particles. Vertical lines guide the eye towards models with good cosmological relic density, whereas horizontal ones represent the “CoGeNT region” and the lower bound of XENON100. Regions where the ${\tau }^{+}{\tau }^{-}$ final state accounts for less than 50% and more than 60% and 80% of the total annihilation channels are shown. We fix $M_S=8\mathrm{GeV}$ and $M_{A_2}=M_{H_2^{+}}=120\mathrm{GeV}$.

Figure 2

Spin-independent dark matter scattering cross section off protons versus annihilation cross section times the relative velocity. Vertical lines bound models with good cosmological relic density whereas horizontal ones represent the CoGeNT region. Regions where the ${\tau }^{+}{\tau }^{-}$ final state accounts for less than 50% and more than 60% and 80% of the total annihilation channels are shown.

Figure 3

Spin-independent DM scattering cross section off protons as a function of the mass of DM with the regions of DAMA/LIBRA (without channeling) [45] and CoGeNT [4] and the sensitivity lines of CDMS and XENON100. For XENON100: (A) corresponds to the collaboration limits [9] and (B) to a sensitivity obtained under different assumptions [10]. For CDMS: (A) is the CDMS limits [47] and (B) corresponds to CDMS-II results [5], disputed in Ref. 10. The blue line (upper, dark grey line) delimits the region where lepton final states start dominating and the green (lower, light grey) one delimits the region where the tau-lepton final state dominates with more than 80%.