A Yukawa coupling parameterization for type I+ II seesaw formula and applications to lepton flavor violation and leptogenesis

In the type I + II seesaw formula the mass matrix of light neutrinos m_nu receives contributions from the exchanges of both heavy Majorana neutrinos and SU(2)_L-triplet Higgs bosons. We propose a new parameterization for the Dirac-type Yukawa coupling matrix of neutrinos in this case, which generalizes the well known Casas-Ibarra parameterization to type I + II seesaw and is useful when the triplet term in m_nu is known. Neutrino masses and mixing, lepton flavor violation in decays like mu -> e \gamma within mSUGRA models and leptogenesis can then be studied within this framework. We illustrate the usefulness of our new parameterization using a number of simple examples.