Abstract
The electron–positron excess reported by the DAMPE collaboration recently may be explained by an electrophilic dark matter (DM). A standard model singlet fermion may play the role of such a DM when it is stabilized by some symmetries, such as a dark U(1)X gauge symmetry, and dominantly annihilates into the electron–positron pairs through the exchange of a scalar mediator. The model, with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively one expects that in this type of models the DM-nucleon cross section should be small since there is no tree-level DM-quark interactions. We however find that at one-loop level, a testable DM-nucleon cross section can be induced for providing ways to test the electrophilic model. We also find that a U(1) kinetic mixing can generate a sizable DM-nucleon cross section although the U(1)X dark photon only has a negligible contribution to the DM annihilation. Depending on the signs of the mixing parameter, the dark photon can enhance/reduce the one-loop induced DM-nucleon cross section.
Highlights
The DAMPE collaboration [1] has reported a direct measurement of the high-energy cosmic-ray electrons and positrons in the energy range 25 GeV to 4.6 TeV with unprecedentedly high energy resolution and low background
A standard model singlet fermion may play the role of such a dark matter (DM) when it is stablized by some symmetries, such as a dark U (1)X gauge symmetry, and dominantly annihilates into the electron-positron pairs through the exchange of a scalar mediator
We find that a U (1) kinetic mixing can generate a sizable DM-nucleon cross section the U (1)X dark photon only has a negligible contribution to the DM annihilation
Summary
The DAMPE collaboration [1] has reported a direct measurement of the high-energy cosmic-ray electrons and positrons in the energy range 25 GeV to 4.6 TeV with unprecedentedly high energy resolution and low background. While large part of the spectrum is well fitted by a smoothly broken power-law model, the spectrum seems to have a narrow bump above the background at around 1.4 TeV [1] This excess indicates the existence of a new source of primary electrons and positrons. In this paper we shall construct an electrophilic DM model in which a DM fermion is stablized by a dark U (1)X gauge group and its Yukawa coupling to a mediator scalar and the standard model (SM) electron works for explaining the DAMPE data. The Yukawa coupling among the DM, the mediator and the electron can always lead to a DM-nucleon scattering at one-loop level. Since the dark photon couples to the SM fermions through a U (1) kinetic mixing, it can generate a DM-nucleon scattering at tree level.
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