Virtual gravitons and brane field scattering in the RS model with a small curvature

The contribution of virtual s-channel Kaluza-Klein (KK) gravitons to high energy scattering of the SM fields in the Randall-Sundrum (RS) model with two branes is studied. The small curvature option of the RS model is considered in which the KK gravitons are narrow low-mass spin-2 resonances. The analytical tree-level expression for a process-independent gravity part of the scattering amplitude is derived, accounting for nonzero graviton widths. It is shown that one cannot get a correct result, if a series of graviton resonances is replaced by a continuous mass distribution, in spite of the small graviton mass splitting. Such a replacement appeared to be justified only in the trans-Planckian energy region.