2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/198727Some results are presented concerning duality invariant effective string actions and the construction of automorphic functions for general (2,2) string compactifications. These considerations are applied in order to discuss the {\it minimal} unification of gauge coupling constants in orbifold compactifications with special emphasis on string threshold corrections.9 pagesHigh Energy Physics - Theorytext