Anomalies on six dimensional orbifolds

We consider localized anomalies in six dimensional Z_n orbifolds. We give avery simple expression for the contribution of a bulk fermion to the fixedpoint gauge anomaly that is independent of the order n of the orbifold twist.We show it can be split into three terms, two of which are canceled by bulkfermions and Green-Schwarz four forms respectively. The remaining anomalycarries an integer coefficient and hence can be canceled by localized fermionsin suitable representations. We present various examples in the context ofsupersymmetric theories. Also we point out that the six-dimensionalgravitational symmetries generally have localized anomalies that requirelocalized four-dimensional fields to transform nontrivially under them.Comment: 49 pages, v2: minor corrections and improvements, matches published versio