Signals for noncommutative QED in eγ and γγ collisions

We study the effects of noncommutative QED (NCQED) in fermion pair production, γ+ γ→f + f̄, and Compton scattering, e+ γ→e + γ. Non-commutative geometries appear naturally in the context of string or M theory and give rise to 3- and 4-point photon vertices and to momentum dependent phase factors in QED vertices which will have observable effects in high energy collisions. We consider e ⁺e ^- colliders with energies appropriate to the TeV linear collider proposals and the multi-TeV CLIC project operating in γγ and eγ modes. Noncommutative scales roughly equal to the center of mass energy of the e ⁺e ^- collider can be probed, with the exact value depending on the model parameters and experimental factors. However, we find that the Compton process is sensitive to Λ _NC values roughly twice as large as those accessible to the pair production process.