Universally leptophilic dark matter from non-Abelian discrete symmetry

The positron anomaly recently reported by the cosmic-ray measurements can be explained by the decaying dark matter scenario, where it decays mainly into leptons with the lifetime of O(1026) s. When the dark matter is a fermionic particle, the lifetime of this order is known to be obtained by a dimension 6 operator suppressed by the unification scale (∼1016GeV), while such decay operators do not necessarily involve only leptons. In addition, the scenario would be spoiled if there exist lower-dimensional operators inducing the dark matter decay. We show in this Letter that a single non-Abelian discrete symmetry such as A4 is possible to prohibit all such harmful (non-leptonically coupled and lower-dimensional) operators. Moreover, the dark matter decays into charged leptons in a flavor-blind fashion due to the non-Abelian flavor symmetry, which results in perfect agreements not only with the PAMELA data but also with the latest Fermi-LAT data reported very recently. We also discuss some relevance between the discrete symmetry and neutrino physics.