Particle horizon and warped phenomenology

Giant resonances of gravity Kaluza–Klein modes (with tensor couplings) in high energy collisions are expected in the Randall–Sundrum orbifold model that incorporates a plausible solution to the hierarchy problem. When the model is extended to incorporate an exponentially small 4-D cosmological constant, the KK spectrum becomes continuous, even in the compactified case. This is due to the presence of a particle horizon, which provides a way to evade Weinbergʹs argument of the need of fine-tuning to get a very small cosmological constant.