Anomaly cancellation in six dimensions

Abstract

It is shown that anomaly cancellation conditions are sufficient to determine the two most important topological numbers relevant for Calabi–Yau (CY) compactification to six dimensions. This reflects the fact that K3 is the only nontrivial CY manifold in two complex dimensions. The Green–Schwarz counterterms are explicitly constructed and sum rules for charges of additional enhanced U(1) factors are derived and the results with all possible Abelian orbifold constructions of K3 are compared. This includes asymmetric orbifolds as well, showing that it is possible to regain a geometrical interpretation for this class of models. Finally, some models with a broken E₇ gauge group which will be useful for more phenomenological applications are discussed herein.