Search for Leptoquarks and FCNC in e+e− annihilations at s=183 GeV

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector. These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 pb−1. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from 134 GeV/c2 to 171 GeV/c2 for electromagnetic type couplings) and couplings of the leptoquark states. A search for top-charm flavour changing neutral currents (e+e−→t̄c or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).