The galactic 511 keV line from MeV milli-charged dark matter

We present a possible explanation of the recently observed 511 keV gamma-ray anomaly with a new `milli-charged' fermion. The new fermion is light (O(10 MeV)) but has never been observed by any collider experiments mainly because of its tiny electromagnetic charge $\epsilon e$. We show that constraints from its relic density in the universe and collider experiments allow a parameter range such that the 511 keV cosmic gamma-ray emission from the galactic bulge may be due to positron production from this O(10 MeV) milli-charged fermion.