  Leptogenesis is usually realized through decays of heavy particles. In this
article we consider another possibility of generating a lepton asymmetry
through annihilations of heavy particles. We demonstrate our idea with a
realistic extension of the standard model containing a heavy doublet and a
light singlet scalars in addition to right-handed neutrinos and Higgs triplets
required for type-I+II seesaw of neutrino masses. We also clarify that this
annihilating leptogenesis scenario can be naturally embedded in more
fundamental theories, like left-right symmetric models or grand unified
theories.
