Two-mediator dark matter models and cosmic electron excess

Abstract

The cosmic electron energy spectrum recently observed by the DAMPE experiment exhibits two interesting features, including a break around 0.9 TeV and a sharp resonance near 1.4 TeV. In this analysis, we propose a dark matter explanation to both exotic features seen by DAMPE. In our model, dark matter annihilates in the galaxy via two different channels that lead to both a narrow resonance spectrum near 1.4 TeV and electron excess events over an extended energy range thus generating the break structure around TeV. The two annihilation channels are mediated by two gauge bosons that interact both with dark matter and with the standard model fermions. Dark matter annihilations through the s-channel process mediated by the heavier boson produce monoenergetic electron-positron pairs leading to the resonance excess. The lighter boson has a mass smaller than the dark matter such that they can be on-shell produced in dark matter annihilations in the galaxy; the lighter bosons in the final state subsequently decay to generate the extended excess events due to the smeared electron energy spectrum in this process. We further analyze constraints from various experiments, including HESS, Fermi, AMS, and LHC, to the parameter space of the model where both excess events can be accounted for. In order to interpret the two new features in the DAMPE data, dark matter annihilation cross sections in the current galaxy are typically much larger than the canonical thermal cross section needed for the correct dark matter relic abundance. This discrepancy, however, is remedied by the nonperturbative Sommerfeld enhancement because of the existence of a lighter mediator in the model.where we use R = 3.5 kpc, α = 2, β = 2 and γ = 0 [63]. The value of ρ s in all the above profiles are chosen such that the local DM density is normalized to ρ χ (8.5 kpc) = 0.39 GeV/cm 3 . We compute the HESS J-factors for these DM profiles using Eq. (6.2) J NFW = 2.25 × 10 21 GeV 2 /cm 5 , J E = 4.41 × 10 21 GeV 2 /cm 5 , J iso = 7.23 × 10 19 GeV 2 /cm 5 .(A.4)HESS collaboration [54] provides the J-factors for two profiles: J NFW = 2.67×10 21 GeV 2 /cm 5 and J E = 4.92 × 10 21 GeV 2 /cm 5 . Thus our calculation here yields slightly smaller J-factors than HESS. We use the J NFW and J E values provided by HESS [54] in the rescaling method to be described in Appendix (B). Because the J-factor for the isothermal profile is not given explicitly by HESS [54], we use our calculated J iso value in the analysis.

Dark matter annihilation into leptons through gravity portals

“…Since the DM particle's mass is about half of the mediator η, namely, m φ ≈ m η /2, the crosssection of DM is enhanced through Breit-Wigner resonance and is sensitive to temperature. Breit-Wigner resonance is the phenomenon that when two particles annihilate through the s-channel, if the total energy of the center-of-mass frame is close to the mass of the propagator, the cross-section will be greatly enhanced [21,54]. The Breit-Wigner resonance has the potential to solve the problem that the thermally averaged cross-section needed to explain the excess of leptons in the cosmic ray is much larger than the cross-section needed to obtain correct DM relic density [20].…”

“…Green's function method [21,65], was used to calculate the contribution of the DM sub-halo to the cosmic electron flux F SH and the contribution of the DM Milky Way halo to the cosmic electron flux F MW : radiation and inverse Compton scattering at energies E > 10 GeV, where the following parameters are adopted: b 0 = 10 −16 GeV/s, D(E) = D 0 (E/GeV) δ is the diffusion coefficient, D 0 = 11 pc 2 /kyr and δ = 0.7, v e is the velocity of the electrons, ρ φ ( x s ) is the DM mass density, and dN/dE s is the energy spectrum of electrons per DM annihilation. It can be checked through the above procedure that the contribution of the Milky Way halo to the cosmic electron flux between 500 GeV and 1500 GeV is two orders of magnitude smaller than the contribution of the DM sub-halo.…”

“…This excess of electrons/positrons in cosmic rays could be a signal from DM [20]. Assuming that there exists a DM sub-halo near the solar system, many groups use specific DM models to explain cosmic electron and positron excess [21][22][23][24][25][26][27][28]. The CALorimetric Electron Telescope (CALET) collaboration also reported the cosmic electron and positron spectrum to range from 11 GeV to 4.8 TeV [29,30].…”

Dark biportals at direct detection

“…Models with both a scalar and a Z portal to the dark sector naturally arise in extensions of the SM gauge group involving a new U (1) [15,16]. A model with two vector mediators was studied in [17] in the context of DM indirect detection. For the case of two scalar mediators, interference effects on LHC searches were studied in [18], while direct detection and associated flavor-physics constraints were discussed in [19,20].…”

Confronting cosmic ray electron and positron excesses with hybrid triplet Higgs portal dark matter

“…The most convincing explanation to this 1.5 TeV excess is based on the assumption that the excess peak is due to DM annihilation (and/or decays) in nearby sub-halo enriched with DM. Various studies have been extensively performed to explain the mentioned electron/position excesses and the possible flavor composition of DM annihilation final states [14][15][16][17][18][19][20][21][22][23][24].…”