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Probing Flavor Structure of Cosmic Ray $e^\mp$ Spectrum and Implications for Dark Matter Indirect Searches

Measuring high energy cosmic ray electrons/positrons (CRE) provides important means for the dark matter (DM) indirect detection and for probing the nearby galactic sources. In this work, we perform a systematic analysis of the flavor structure of DM annihilations into charged leptons based on the cosmic ray CRE spectra measured by DAMPE, Fermi-LAT, AMS-02, and CALET experiments. We study the annihilations of possible TeV scale DM particles in a nearby subhalo, which is proposed to explain the possible peak-like structure of the DAMPE CRE data. We pay special attention to the possible non-resonant excess (besides the possible peak-like structure) and demonstrate that such non-resonant excess can mainly arise from the decay of muons produced by the DM annihilations in the subhalo. With these we study the flavor composition of the lepton final states from DM annihilations $χχ\to e^+e^-, μ^+μ^-, τ^+τ^-$ by fitting the CRE data. We demonstrate that decays of the final states $μ^+ μ^-$ and $τ^+ τ^-$ can provide the non-resonant excess, while the peak excess arises from the $e^+ e^-$ final state. We further analyze the constraints on the lepton flavor composition using the Fermi-LAT $γ$-ray measurements. We find that the flavor composition is consistent with the Fermi-LAT data at relatively low Galactic latitudes, while the fraction of the final state $τ^\pm$ is severely bounded.