  We discuss the theory and phenomenology of the interplay between the massless
graviton and its massive Kaluza-Klein modes in the Randall-Sundrum two-brane
model. The equations of motion of the transverse traceless degrees of freedom
are derived by means of a Green function approach as well as from an effective
nonlocal action. The second procedure clarifies the extraction of the particle
content from the nonlocal action and the issue of its diagonalization. The
situation discussed is generic for the treatment of two-brane models if the
on-brane fields are used as the dynamical degrees of freedom. The mixing of the
effective graviton modes of the localized action can be interpreted as
radion-induced gravitational-wave oscillations, a classical analogy to meson
and neutrino oscillations. We show that these oscillations arising in
M-theory-motivated braneworld setups could lead to effects detectable by
gravitational-wave interferometers. The implications of this effect for models
with ultra-light gravitons are discussed.
