Leptophilic-portal dark matter in the light of AMS-02 positron excess

We revisit dark matter annihilation as an explanation of the positron excess reported recently by the AMS-02 satellite-borne experiment. To this end, we propose a particle dark matter model by considering a two Higgs doublet model (2HDM) extended with an additional singlet boson and a singlet fermion. The additional (light) boson mixes with the pseudoscalar inherent in the 2HDM, and the singlet fermion, which is the dark matter candidate, annihilates via this bosonic portal. The dark matter candidate is made leptophilic by choosing the lepton-specific 2HDM and a suitable high value of tan beta. We identify the model parameter space which explains the muon g-2 anomaly while evading the experimental constraints. After establishing the viability of the singlet fermion to be a dark matter candidate, we calculate the positron excess produced from its annihilation to the light bosons which primarily decay to muons. Incorporating the Sommerfeld effect caused by the light mediator and an appropriate boost factor, we find that our proposed model can satisfactorily explain the positron fraction excess as well as the positron spectrum data reported by the AMS-02 experiment.

Automated summary

The study proposes a dark matter model with an additional singlet boson and a singlet fermion to explain the positron excess reported by the AMS-02 satellite experiment. By mixing the additional (light) boson with the singlet fermion, the dark matter candidate annihilates through this bosonic portal. The model can successfully account for the positron fraction excess as well as the positron spectrum data reported by the AMS-02 experiment by considering various factors such as the Sommerfeld effect and appropriate boost factors.