CONSTRAINTS ON THE UNIVERSAL CONTACT INTERACTION

Forces beyond those of the standard model may manifest themselves at l ow energies as four-fermion contact interactions. If these new forces are independent of colour and flavour quantum numbers including baryon and lepton number, then all low energy constraints, arising from quar k-lepton universality, flavour-changing neutral currents and atomic pa rity violation are evaded. This is due to the global U(45) symmetry wh ich the standard model exhibits in the limit of vanishing gauge and Yu kawa couplings. The corresponding contact interaction is a unique curr ent-current interaction. Constraints from LEP2 imply that this univers al contact interaction cannot be the origin of the recently observed h igh-Q(2) events at HERA. (C) 1997 Published by Elsevier Science B.V.