Large Neutrino Mixings in MSSM and SUSY GUTs: Democratic Approach.

We show how, with aid from a U (1) flavor symmetry, the hierarchical structure in the charged fermion sector and a democratic approach for neutrinos that yields large solar and atmospheric neutrino mixings can be simultaneously realized in the MSSM framework. In SU(5), due to the unified multiplets, we encounter difficulties. Namely, democracy for the neutrinos leads to a wrong hierarchical pattern for charged fermion masses and mixings. We discuss how this is overcome in flipped SU(5). We then proceed to an example based on 5D SUSY SU(5) GUT in which the neutrino democracy idea can be realized. A crucial role is played by bulk states, the so-called ‘copies’, which are split by compactifying the fifth dimension on an S(1)/Z2 × Z′2 orbifold. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]