2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/137924Following the recent exploration of smooth heterotic compactifications with unitary bundles, orbifold compactifications in six dimensions can be shown to correspond in the blow-up to compactifications with U(1) gauge backgrounds. A powerful tool is the comparison of anomaly polynomials. The presentation here focuses on heterotic SO(32) compactifications in six dimensions including five-branes. Four dimensional and E8 x E8 models are briefly commented on.Submitted for the SUSY07 proceedings, 4 pages, LaTeXHigh Energy Physics - Theorytext