Bounds on Scalar Leptoquarks from Z Physics
  We analyse the constraints on scalar leptoquarks coming from radiative corrections to $Z$ physics. We perform a global fitting to the LEP data including the contributions of the most general effective Lagrangian for scalar leptoquarks, which exhibits the $SU(2)_L \times U(1)_Y$ gauge invariance. We show that the bounds on leptoquarks that couple to the top quark are much stronger than the ones obtained from low energy experiments. 
J.K. Mizukoshi (IFUSP), O.J.P. Eboli (CERN), and M.C. Gonzalez-Garcia   (CERN)