Unparticle effects in photon–photon scattering

Elastic photon–photon scattering can occur in the Standard Model only via loop diagrams and is naturally suppressed. Unparticle can induce tree-level photon–photon scattering through the operator FμνFμνOUFμνFμνOU for spin-0 unparticle or FμαFανOUμν for spin-2 unparticle. Due to the peculiar CP-conserving phase exp(−idUπ)exp(−idUπ) associated with the time-like unparticle propagator for non-integral scaling dimension dUdU, the interference effects of the s-channel amplitude with the t- and u-channels ones on the total cross sections as well as the angular distributions are found to be of some significance. We found that the matrix-element squared is independent of whether we used the transverse form or the conformal form for the spin-2 unparticle propagator. In addition, we show that the cross sections via unparticle exchange can be substantially larger than the Standard Model contribution.