  We demonstrate that if the dark matter (DM) in the Universe contains multiple
components,the interactions between the DM components may induce DM
conversions. It is then possible that the lightest DM component with an
annihilation cross section much larger than that of the typical weakly
interacting massive particle (WIMP) can obtain a relic density in consistent
with the cosmological observations, due to an enhancement from the DM
conversion process at late time after the thermal decoupling. This provides an
alternative source of large boost factor required to explain the excesses
reported by the recent DM indirect search experiments.
