Radion effects on unitarity in gauge-boson scattering - art. no. 076003

The scalar field associated with fluctuations in the positions of the two b ranes, the "radion," plays an important role in determining the cosmology a nd collider phenomenology of the Randall-Sundrum solution to the hierarchy problem. It is now well known that the radion mass is on the order of a wea k 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 vect or boson scattering amplitudes to explore the constraints on the radion mas s and its coupling from perturbative unitarity. The scattering cross sectio n can indeed become nonperturbative at energies prior to reaching the TeV b rane cutoff scale, but only when some curvature-Higgs mixing on the TeV bra ne is present. We show that the coefficient of the curvature-Higgs mixing o perator must be less than about 3 for the 4D effective theory to respect pe rturbative unitarity up to the TeV brane cutoff scale. Mass bounds on the H iggs boson and the radion are also discussed.