Bulk and brane anomalies in six dimensions

We study anomalies of six-dimensional gauge theories compactified on orbifolds. In addition to the known bulk anomalies, brane anomalies appear on orbifold fixpoints in the case of chiral boundary conditions. At a fixpoint, where the bulk gauge group G is broken to a subgroup H, the non-abelian G-anomaly in the bulk reduces to a H-anomaly which depends in a simple manner on the chiral boundary conditions. We illustrate this mechanism by means of a SO(10) GUT model.