2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188402We 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 SU(N) gauge group (N >= 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.Comments added, version to appear in Physical Review D (v3); References added (v2); 19 pages (v1)High Energy Physics - Phenomenologytext