Radiative Neutrino Mass, Dark Matter and Leptogenesis

We propose an extension of the standard model, in which neutrinos are Dirac particles and their tiny masses originate from a one-loop radiative diagram. The new fields required by the neutrino mass-generation also accommodate the explanation for the matter-antimatter asymmetry and dark matter in the universe.Comment: 4 pages, 3 figures. Revised version with improved model. Accepted by PR

A left-right symmetric model with SU(2)-triplet fermions

We consider an $SU(3)_c \otimes SU(2)_L \otimes SU(2)_R \otimes U(1)_{B-L}$ left-right symmetric model with three Higgs scalars including an $SU(2)_L$ doublet, an $SU(2)_R$ doublet and an $SU(2)_L \otimes SU(2)_R$ bidoublet. In addition to usual SU(2)-doublet fermions, our model contains SU(2)-triplet fermions with Majorana masses. The neutral components of the left-handed triplets can contribute a canonical seesaw while the neutral components of the right-handed triplets associated with the right-handed neutrinos can contribute a double/inverse-type seesaw. Our model can be embedded into an SO(10) grand unification theory where the triplets belong to the $45=(1,3,1,0) \oplus (1,1,3,0)\oplus ...$ representations.Comment: 4 pages. To appear in Phys. Rev.

Neutrino masses, leptogenesis and dark matter in hybrid seesaw

We suggest a hybrid seesaw model where relatively ``light''right-handed neutrinos give no contribution to the neutrino mass matrix due to a special symmetry. This allows their Yukawa couplings to the standard model particles to be relatively strong, so that the standard model Higgs boson can decay dominantly to a left and a right-handed neutrino, leaving another stable right-handed neutrino as cold dark matter. In our model neutrino masses arise via the type-II seesaw mechanism, the Higgs triplet scalars being also responsible for the generation of the matter-antimatter asymmetry via the leptogenesis mechanism.Comment: 4 page

Radiative seesaw in left-right symmetric model

There are some radiative origins for the neutrino masses in the conventional left-right symmetric models with the usual bi-doublet and triplet Higgs scalars. These radiative contributions could dominate over the tree-level seesaw and could explain the observed neutrino masses.Comment: 5 pages, 3 figures. Revised version with minor change. Accepted by PR

Resonant Leptogenesis and Verifiable Seesaw from Large Extra Dimensions

In the presence of large extra dimensions, the fundamental scale could be as low as a few TeV. This yields leptogenesis and seesaw at a TeV scale. Phenomenologically two TeV-scale Majorana fermions with a small mass split can realize a resonant leptogenesis whereas a TeV-scale Higgs triplet with a small trilinear coupling to the standard model Higgs doublet can give a verifiable seesaw. We propose an interesting scenario where the small parameters for the resonant leptogenesis and the type-II seesaw can be simultaneously generated by the propagation of lepton number violation from distant branes to our world.Comment: 5 pages. More discussions and references. Published in PR

Relations between Neutrino and Charged Fermion Masses

We find an intriguing relation between neutrino and charged fermion masses, $|m_{\nu_3^{}}^2- m_{\nu_1^{}}^2| : (m_{\nu_2^{}}^2- m_{\nu_1^{}}^2):: V_{tb}^4 m_\tau^2 m_b^2/m_t^2 : V_{cs}^4 m_\mu^2 m_s^2/m_c^2$. We further indicate this relation can be predicted by a left-right symmetric model.Comment: 4 pages, 1 figure. Model is slightly corrected. Title is changed. Journal versio