SU(8) GUT revisited: The Eightfold Way for composite quarks and leptons

The $L$-$R$ symmetric composite model for quarks and leptons where constituent preons possessing some local $SU(N)_{MF}$ metaflavor symmetry are bound by the chiral $SO(n)_{L}\times SO(n)_{R}$ gauge metacolor forces is considered. We find properly strengthening the 't Hooft's anomaly matching condition that just the eight left-handed and right-handed preons and their global chiral symmetry $SU(8)_{L}\times SU(8)_{R}$ may determine physical world at small distances that uniquely identifies the local metaflavor symmetry $SU(8)_{MF}$ as its basic unified symmetry. We next show that an appropriate $L$-$R$ symmetry violation reduces the $SU(8)_{MF}$ theory down to the conventional $SU(5)$ GUT with an extra local family symmetry $SU(3)_{F}$ and three standard generations of quarks and leptons. Though the tiny radius of compositeness for universal preons composing both quarks and leptons makes it impossible to immediately confirm their composite nature, a few special $SU(5)\times SU(3)_{F}$ multiplets of extra composite fermions located at the scales from $O(1)$ $TeV$ up to the Planck mass scale predicted by the theory may appear of actual experimental interest. Some of them can be directly observed, the others populate the $% SU(5)$ GUT desert. Due to their mixing with ordinary quark-lepton families there may arise a marked violation of unitarity in the mass matrices for leptons and down quarks depending on the interplay between the compositeness scale and scale of the family symmetry $SU(3)_{F}$.