Orbifold family unification

Abstract

We study the possibility of complete family unification in higher-dimensional space-time. Three families of matters in $SU(5)$ grand unified theory are derived from a single bulk multiplet of the $SU(N)$ gauge group ($N\ensuremath{\ge}9$) in the framework of ${S}^{1}/{Z}_{2}$ orbifold models. In the case of the direct orbifold breaking down to the standard model gauge group, there are models in which bulk fields from a single multiplet and a few brane fields compose three families of quarks and leptons.