Toric Genera of Homogeneous Spaces and their Fibrations

The aim of this paper is to further study the universal toric genus of compact homogeneous spaces and their homogeneous fibrations. We consider the homogeneous spaces with positive Euler characteristic. It is well known that such spaces carry many stable complex structures equivariant under the canonical action of the maximal torus T^k. As the torus action in this case only has isolated fixed points it is possible to effectively apply localization formula for the universal toric genus. Using this, we prove that the famous topological results related to rigidity and multiplicativity of a Hirzebruch genus can be obtained on homogeneous spaces just using representation theory. In this context, for homogeneous SU-spaces, we prove the well-known result about rigidity of the Krichever genus. We also prove that for a large class of stable complex homogeneous spaces any T^k-equivariant Hirzebruch genus given by an odd-power series vanishes. With regard to the problem of multiplicativity, we provide construction of stable complex T^k-fibrations for which the universal toric genus is twistedly multiplicative. We prove that it is always twistedly multiplicative for almost complex homogeneous fibrations and describe those fibrations for which it is multiplicative. As a consequence for such fibrations the strong relations between rigidity and multiplicativity for an equivariant Hirzebruch genus is established. The universal toric genus of the fibrations for which the base does not admit any stable complex structure is also considered. The main examples here for which we compute the universal toric genus are the homogeneous fibrations over quaternionic projective spaces.