Flexibility of Group Actions on the Circle

In this partly expository work, a framework is developed for building exotic circle actions of certain classical groups.

The authors give general combination theorems for indiscrete isometry groups of hyperbolic space which apply to Fuchsian and limit groups. An abundance of integer-valued subadditive defect-one quasimorphisms on these groups follow as a corollary.

The main classes of groups conside...