Smooth toral actions on principal bundles and characteristic classes.
The purpose of our work is to find explicit formulae for the computation of some characteristic classes of smooth principal bundles P: P --> B, in terms of local invariants at a singular subset AG of B, associated to a smooth action of a compact Lie group G on P. This singular subset, AG, is defined as the set of points x in B whose isotropy subgroups Gx have dimension at least one.