General vacuum stability of orbifold gauge breaking and application to asymptotic grand unification

We examine the vacuum stability of gauge symmetry breaking in five dimensions, compactified on the S1/(Z2×Z2′) orbifold. We consider SU(N), Sp(N), SO(2N), and SO(2N+1) theories in the bulk, and provide an exhaustive classification of possible parity assignments that lead to stable orbifolds and of the corresponding symmetry breaking patterns. We use these results in the search for viable asymptotic grand unification theories (aGUT), testing the stability criteria on models based on SU(6) and SU(8). As a result, we identify two viable aGUTs: a unique SU(6) pathway down to the Standard Model, and one SU(8) model leading to an intermediate Pati-Salam partial unification.