Annihilating leptogenesis

Leptogenesis is usually realized through decays of heavy particles. In this Letter 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.