A Simple-Minded Unitarity Constraint and an Application to Unparticles

Understand

Unitarity, a powerful constraint on new physics, has not always been properly accounted for in the context of hidden sectors.

• Feng, Rajaraman and Tu have suggested that large (pb to nb) multi-photon or multi-lepton sugnals could be generated at the LHC through the three-point functions of a conformally-invariant hidden sector (an "unparticle" sector.) Because of the conformal invariance, the kinematic distributions are calculable.
• However, the cross-sections for many such processes grow rapidly with energy, and at some high scale, to preserve unitarity, conformal invariance must break down.
• Requiring that conformal invariance not be broken, and that no signals be already observed at the Tevatron, we obtain a strong unitarity bound on multi-photon events at the (10 TeV) LHC.