The quark–lepton mass problem and the ideas of mass protection are reviewed. The hierarchy problem and suggestions for its resolution, including Little Higgs models, are discussed. The Multiple Point… Expand

Four simple but realistic patterns of quark mass matrices are derived from orbifold models of superstring theory in the absence of gauge symmetries. Two of them correspond to the Ramond–Roberts–Ross… Expand

The standard model can be interpreted as the leading order of a Low-Energy Effective Theory (LEET) invariant under a higher non linearly realized symmetry Snat ⊃ SU(2)W × U(1)Y equipped with a… Expand

Flavor-changing neutral currents are reconsidered allowing the possibility that superheavy quarks, with masses comparable to the weak-boson mass, exist in nature. It is argued that the natural… Expand

In theories with spontaneously broken gauge symmetries, various masses, or mass differences may vanish in zeroth order as a consequence of the representation content of the fields appearing in the… Expand

In theories with spontaneously broken local symmetries, renormalizability sometimes forces the scalar field interactions to have a larger group of symmetries than the gauge field interactions.… Expand