Three-Generat ion Models from Global Gauge Anomaly-Free Theories

In this work, we show how a global gauge anomaly of a gauge group H can be computed from a local one of a larger gauge group G ⊃ H. We also show that the number f of generations is tied to the consistency of a gauge theory H with initially a Z_f gIobal gauge anomaly. We give some examples of SU(N) models, in different dimensions of spacetime, with three families.