It is argued with the help of an illustrative model, that the inter– species hierarchy among the fermion masses and the quark mixing angles can be accommodated naturally in the standard model with (approximate) flavor democracy provided there are four families of sequential quark–leptons with all members of the fourth family having roughly equal masses. The special problem of light neutrino mas...

Exact, analytic expressions for the valence band effective masses in the spin-orbit, spds* empirical tight-binding model are derived. These expressions together with an automated fitting algorithm are used to produce improved parameter sets for Si and Ge at room temperature. Detailed examinations of the analytic effective-mass expressions reveal critical capabilities and limitations of this mod...