Abstract
The Standard Model (SM) supplemented by Type II Seesaw and a SM gauge-singlet scalar dark matter (DM) is a very simple framework to incorporate the observed neutrino oscillations and provide a plausible DM candidate. In this framework, the scalar DM naturally has a leptophilic nature with a pair annihilating mainly into the SM SU(2)$_L$ triplet Higgs scalar of Type II Seesaw which, in turn, decay into leptons. In this work, we consider indirect signatures of this leptophilic DM and examine the spectrum of the cosmic ray electron/positron flux from DM pair annihilations in the Galactic halo. Given an astrophysical background spectrum of the cosmic ray electron/positron flux, we find that the contributions from DM annihilations can nicely fit the observed data from the AMS-02, DAMPE and Fermi-LAT collaborations, with a multi-TeV range of DM mass and a boost factor for the DM annihilation cross section of ${\cal O}(1000)$. The boost factor has a slight tension with the Fermi-LAT data for gamma-ray from dwarf spheroidal galaxies, which can be ameliorated with an enhanced local DM density by a factor of about 2.
Highlights
The existence of dark matter (DM) in the Universe has been established by a variety of cosmological and astronomical observations
Type II seesaw extension of the standard model (SM) with a SM gaugesinglet scalar DM is a simple framework to supplement the SM with the desired neutrino mass matrix and a plausible DM candidate
We have calculated the spectrum of the cosmic ray electron/positron flux from DM pair annihilations in the Galactic halo
Summary
The existence of dark matter (DM) in the Universe has been established by a variety of cosmological and astronomical observations. The nature of DM is still unknown and stands as one of the biggest mysteries in particle physics and cosmology. As cosmic ray observations become more and more precise, a deviation (excess) of an observed cosmic ray flux from its astrophysical prediction can be used to learn about the nature of DM particles. The latest and most precise measurements of the cosmic ray electron and positron (CRE) flux have been reported by the AMS-02 [1], DAMPE [2], and Fermi-LAT [3] collaborations. The increase of the positron spectrum above 100 GeV and the break of the CRE spectrum around 1 TeV are unexpected results from these measurements, possibly indicating an excess of the CREs originating from DM particles
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