  Following up on our recent study, we consider the regime of graviton masses
and gravitational wave propagation distances at which decoherence of the wave
packets plays a major role for phenomenology. This regime is of particular
interest, as it can lead to very striking phenomena of echo events in the
gravitational waves coming from coalescence events. The power of the
experimental search in this case lies in the fact that it becomes sensitive to
a large range of graviton masses, while not relying on a specific production
mechanism. We are thus able to place new relevant limits on the parameter space
of the graviton mixing angle.
