The scalar field associated with fluctuations in the positions of the two branes, the ``radion'', plays an important role determining the cosmology and collider phenomenology of the Randall-Sundrum solution to the hierarchy problem. It is now well known th

a r X i v :h e p -p h /0104074v 1 6 A p r 2001hep-ph/0104074

MADPH–01–1219

Radion effects on unitarity in gauge-boson scattering

Tao Han,Graham D.Kribs,and Bob McElrath Department of Physics,University of Wisconsin,1150University Ave.,Madison,WI 53706-1390than@pheno.physics.wisc.edu,kribs@pheno.physics.wisc.edu,mcelrath@pheno.physics.wisc.edu Abstract The scalar field associated with fluctuations in the positions of the two branes,the “ra-dion”,plays an important role determining the cosmology and collider phenomenology of the Randall-Sundrum solution to the hierarchy problem.It is now well known that the radion mass is of order the weak scale,and that its couplings to standard model fields are order O (TeV −1)to the trace of the energy momentum tensor.We calculate longitudinal vector

boson scattering amplitudes to explore the constraints on the radion mass and its coupling from perturbative unitarity.The scattering cross section can indeed become non-perturbative at energies prior to reaching the TeV brane cutoffscale,but only when some curvature-Higgs mixing on the TeV brane is present.We show that the coefficient of the curvature-Higgs mixing operator must be less than about 3for the 4-d effective theory to respect perturbative unitarity up to the TeV brane cutoffscale.Mass bounds on the Higgs boson and the radion are also discussed.