Family Unification with SO(10)

Unification based on the group SO(10)^3 \times S_3 is studied. Each family has its own SO(10) group, and the S_3 permutes the three families and SO(10) factors. This is the maximal local symmetry for the known fermions. Family unification is achieved in the sense that all known fermions are in a single irreducible multiplet of the symmetry. The symmetry suppresses SUSY flavor changing effects by making all squarks and sleptons degenerate in the symmetry limit. Doublet-triplet splitting can arise simply, and non-trivial structure of the quark and lepton masses emerges from the gauge symmetry, including the "doubly lopsided" form.Comment: 11 pages, references adde

Classification of Effective Neutrino Mass Operators

We present a classification of SU(3) x SU(2) x U(1) gauge invariant \Delta L = 2 (L being lepton number) effective operators relevant for generating small Majorana neutrino masses. Operators of dimension up to 11 have been included in our analysis. This approach enables us to systematically identify interesting neutrino mass models. It is shown that many of the well-known models fall into this classification. In addition, a number of new models are proposed and their neutrino phenomenology is outlined. Of particular interest is a large class of models in which neutrinoless double beta decays arise at a lower order compared to the neutrino mass, making these decays accessible to the current round of experiments.Comment: 34 pages in RevTeX with 18 figure

Z_3 Dark Matter and Two-Loop Neutrino Mass

Dark matter is usually distinguished from ordinary matter by an odd-even parity, i.e. the discrete symmetry Z_2. The new idea of Z_3 dark matter is proposed with a special application to generating radiative Majorana neutrino masses in two-loop order.Comment: expanded (9 pages, 2 figures), 2 references adde

Higher-dimensional operators in SUSY SO(10) GUT models

SO(10) GUT models with only small Higgs fields use higher-dimensional operators to generate realistic fermion mass matrices. In particular, a Higgs field in the spinor representation, 16^d_H, acquires a weak scale vev. We include the weak vev of the corresponding field \bar{16}^u_H and investigate the effect on two successful models, one by Albright and Barr (AB) and another by Babu, Pati and Wilczek (BPW). We find that the BPW model is a particular case within a class of models with identical fermion masses and mixings. In contrast, we expect corrections to the parameters of AB-type models.Comment: 3 page

Perturbative SO(10) GUT and the Minimal Higgs Sector

The breaking of SO(10) to SU(3)_C x U(1)_EM can be accomplished by just four Higgs fields: the symmetric rank-two tensor, S(54); a pair of spinors, C(16) and Cbar(16bar); and a vector, T(10). This setup is also able to generate realistic fermion masses. The heavy color triplets in the vector and spinor fields mediate proton decay via dimension-five operators. The experimental bounds on proton decay constrain the structure and size of the Yukawa operators.Comment: v2: discussion about gauge coupling unification extended; figure added; to appear in Phys. Lett.