2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/51561We study four dimensional $Z_2 \times Z_2$ (shift)-orientifolds in presence of internal magnetic fields and NS-NS $B$-field backgrounds, describing in some detail one explicit example with N=1 supersymmetry. These models are related by $T$-duality to orientifolds with $D$-branes intersecting at angles and exhibit, due to the background fields, a rank reduction of the gauge group and multiple matter families. Moreover, the low-energy spectra are chiral and anomaly free if $D5$-branes are present along the magnetized directions.LaTeX file, 8 pages, based on the talk presented at the ``First International Conference On String Phenomenology'', Oxford, 6-11 july 2002. Eq.(1) and table 3 corrected. 1 reference addedHigh Energy Physics - Theorytext