Quasi-invariant states with uniformly bounded cocycles

We investigate the notion of quasi-invariant states introduced in [2, 3] from an analytic viewpoint.We give the structures of quasi-invariant states with uniformly bounded cocycles. As a consequence, we can apply a Theorem of Kovacs and Szucs to get a conditional expectation on fixed points and another of Stormer to get an invariant semifinite trace under extra assumptions.