Constraints from precision electroweak data on leptoquarks and bileptons

Explicit expressions are derived for the oblique parameters S and T in certain extensions of the standard model. In particular, we consider leptoquarks and bileptons, and find phenomenological constraints on their allowed masses. Leptoquarks suggested by the neutral and charged current anomalies at DESY HERA can give improved agreement with both S and T. If bileptons are the only new states, the singly charged one must be heavier than the directly established lower limit. Finally, we study SU(15) grand unification and show that there are legions of parameter space where the theory is compatible with experimental data. [S0556-2821(98)06719-8]