Leptoquarks At Future Lepton Colliders

Introduction and Background The observation of a possible excess of both neutral and charged current events at HERA 1 has brought the discussion of leptoquarks(LQs) and their properties off the back burner, though they have been subjects of study for quite some time. 2;3 For more than a decade any discussion of leptoquark models has been historically based on the classic work by Buchmuller, Ruckl and Wyler (BRW). 2 As these authors showed, LQs can be either spin-0 (scalars) or spin-1 (vectors) and may carry fermion number, F = 3B + L = 0 or \Sigma2. In that paper the authors provided a set of basic assumptions under which consistent leptoquark models can be constructed; these can be restated as: (a) LQ couplings must be invariant with respect to the Standard Model (SM) gauge interactions, (b) LQ interactions must be renormalizable, (c) LQs coupl