Single- and multi-photon production in e⁺e^- collisions at a centre-of-mass energy of 183 GeV

The production of final states involving one or more energetic photons from e⁺e^- collisions is studied in a sample of 58.5 pb^-1 of data recorded at a centre-of-mas s energy of 183 GeV by the ALEPH detector at LEP. The e⁺e^- → νν̄γ(γ) and e⁺e^- → γγ(γ) cross sections are measured. The data are in good agreement with predictions based on the Standard Model and are used to set upper limits on the cross sections for anomalous photon production in the context of two supersymmetric models and for various extensions to QED. In particular, in the context of a super-light gravitino model a cross section upper limit of 0.38 pb is placed on the process e⁺e^- → G̃G̃γ, allowing a lower limit to be set on the mass of the gravitino. Limits are also set on the mass of the lightest neutralino in Gauge Mediated Supersymmetry Breaking models. In the case of equal ee*γ and eeγ couplings a 95% C.L. lower limit on M_e* of 250GeV/c² is obtained.