2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148097By including the effects of superstring thresholds, we reconsider minimal string unification together with the requirement of producing a supersymmetry-breaking gluino condensate in the hidden sector. This gives, for examples of phenomenologically-viable $Z_8'$ and other related orbifolds, the constraint that $0.1215 \leq α_s(M_Z) \leq 0.1270$. In such models, a hidden photino can be a source of cosmological dark matter detectable by gravitational microlensing.12 pages (23k), in ReVTeX plus 3 postscript figures (27k), Submitted to Physical Review LettersHigh Energy Physics - Phenomenologytext