The Need for a Photon-Photon Collider in addition to LHC & ILC for   Unraveling the Scalar Sector of the Randall-Sundrum Model
  In the Randall-Sundrum model there can be a rich new phenomenology associated with Higgs-radion mixing. A photon-photon collider would provide a crucial complement to the LHC and a future ILC collider for fully determining the parameters of the model and definitively testing it. 
John F. Gunion (U.C. Davis)