Leptonic dark matter annihilation in the evolving universe: constraints
  and implications
  The cosmic electron and positron excesses have been explained as possible
dark matter (DM) annihilation products. In this work we investigate the
possible effects of such a DM annihilation scenario during the evolution
history of the Universe. We first calculate the extragalactic $\gamma$-ray
background (EGRB), which is produced through the final state radiation of DM
annihilation to charged leptons and the inverse Compton scattering between
electrons/positrons and the cosmic microwave background. The DM halo profile
and the minimal halo mass, which are not yet well determined from the current
N-body simulations, are constrained by the EGRB data from EGRET and Fermi
telescopes. Then we discuss the impact of such leptonic DM models on cosmic
evolution, such as the reionization and heating of intergalactic medium,
neutral Hydrogen 21 cm signal and suppression of structure formation. We show
that the impact on the Hydrogen 21 cm signal might show interesting signatures
of DM annihilation, but the influence on star formation is not remarkable.
Future observations of the 21 cm signals could be used to place new constraints
on the properties of DM.
