Non-Abelian gauge family symmetry in rank-8 and -16 grand-unified string theories

Abstract

One of the main points of the investigations in high-energy physics is to study the next chain: a law of the quark and lepton mass spectra→the puzzles of the quark and lepton family mixing→a possible new family dynamics. The new family symmetry dynamics might be connected to the existence of some exotic gauge or matter fields or something else. For this it will better to study the possibilities of the appearance of this gauge symmetry in the framework of the Grand-Unified String Theories. In the framework of four-dimensional heterotic superstring with free fermions we investigate the rank-eight Grand-Unified String Theories (GUST) which contain theSU(3)H-gauge family symmetry. We explicitly construct GUST with gauge symmetryG=SU(5)×U(1)×(SU(3)×U(1))H andG=SO(10)×(SU(3)×U(1))H⊃SO(16) orE(6)×SU(3)H⊃E(8) in free complex fermion formulation. As the GUSTs originating from Kac-Moody algebras (KMA) contain only low-dimensional representations it is usually difficult to break the gauge symmetry. We solve this problem taking for the observable gauge symmetry the diagonal subgroupG symm of rank-16 groupG×G⊃SO(16)×SO(16) or (E(6)×SU(3)H)2 ⊃E(8)×E(8). We discuss the possible fermion matter and Higgs sectors in these models. In these GUST there has to exist «superweak» light chiral matterm H <M W). The understanding of quark and lepton mass spectra and family mixing leaves a possibility for the existence of an unusually low-mass breaking scale of theSU(3)H family gauge symmetry (some TeV).