Signals for Non-Commutative QED in e γ and γ γ Collisions

We study the effects of non-commutative QED (NCQED) in fermion pair production, gamma + gamma -> f + bar{f} and Compton scattering, e + gamma -> e + gamma. Non-commutative geometries appear naturally in the context of string/M-theory and gives 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 gamma gamma and e gamma modes. Non-commutative 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 found that the Compton process is sensitive to Lambda_{NC} values roughly twice as large as those accessible to the pair production process.