Abstract
The cosmic electron and positron excesses have been explained aspossible dark matter (DM) annihilation products. In this work weinvestigate the possible effects of such a DM annihilation scenarioduring the evolution history of the Universe. We first calculate theextragalactic γ-ray background (EGRB), which is producedthrough the final state radiation of DM annihilation to chargedleptons and the inverse Compton scattering betweenelectrons/positrons and the cosmic microwave background. The DM haloprofile and the minimal halo mass, which are not yet well determinedfrom the current N-body simulations, are constrained by the EGRBdata from EGRET and Fermi telescopes. Then we discuss the impact ofsuch leptonic DM models on cosmic evolution, such as thereionization and heating of intergalactic medium, neutral Hydrogen21 cm signal and suppression of structure formation. We show thatthe impact on the Hydrogen 21 cm signal might show interestingsignatures of DM annihilation, but the influence on star formation isnot remarkable. Future observations of the 21 cm signals could beused to place new constraints on the properties of DM.
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