Search

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 β. 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. [ABSTRACT FROM AUTHOR]

We propose a two component dark matter setup by extending the Standard Model with a singlet and a hyperchargeless triplet scalars, each of them being odd under different Z2 symmetries. We observe that the interconversion between the two dark matter components allow a viable parameter space where masses of both the dark matter candidates can be below TeV, even though their individual contribution to single component dark matter rules out any such sub-TeV dark matter. We find that a lighter mass of the neutral component of the scalar triplet, playing the role of one dark matter component, compared to the singlet one is favored. In addition, the setup is shown to make the electroweak vacuum absolutely stable till the Planck scale, thanks to Higgs portal coupling with the scalar dark matter components. [ABSTRACT FROM AUTHOR]

We present a study of singlet-doublet vectorlike leptonic dark matter (DM) in the framework of the two-Higgs-doublet model (2HDM), where the dark sector is comprised of one doublet and one singlet vectorlike fermion (VLF). The DM, that arises as an admixture of the neutral components of the VLFs, is stabilized by an imposed discrete symmetry Z'2. We test the viability of the DM candidate in the light of observations from Planck and recent limits on spin-independent direct detection experiments and search for its possible collider signals. In addition, we also look for the stochastic gravitational wave (GW) signatures resulting from strong first-order phase transition due to the presence of the second Higgs doublet. The model thus offers a viable parameter space for a stable DM candidate that can be probed from direct search, collider, and GW experiments. [ABSTRACT FROM AUTHOR]

We extend the so-called singlet doublet dark matter model, where the dark matter is an admixture of a Standard Model singlet and a pair of electroweak doublet fermions, by a singlet scalar field. The new portal coupling of it with the dark sector not only contributes to the dark matter phenomenology (involving relic density and direct detection limits) but also becomes important for generation of dark matter mass through its vacuum expectation value. While the presence of dark sector fermions affects the stability of the electroweak vacuum adversely, we find this additional singlet is capable of making the electroweak vacuum absolutely stable up to the Planck scale. A combined study of dark matter phenomenology and the Higgs vacuum stability issue reflects that the scalar sector mixing angle can be significantly constrained in this scenario. [ABSTRACT FROM AUTHOR]