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 $S_1\mathrm{/}({\mathbb{Z}}_2\times {\mathbb{Z}}_2^{\mathrm{\prime }})$ 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.