Flavour violation, scalar particles and leptoquarks

Abstract

General features of neutral Higgs particle-fermion Yukawa couplings, including the relation of these couplings to the charge of the fermion, are discussed. Mass bounds on neutral Higgs particles from different flavour-changing processes are calculated. The KL − KL mass difference gives the most stringent bound of 150 TeV. Flavour-changing processes mediated by leptoquarks are also studied. μe conversion and KL decays give comparable bounds, of order 1–10 TeV for pseudoscalar leptoquarks occurring in technicolour models and of order 10–90 TeV for vector leptoquarks occurring in the Pati-Salam type of grand unification models. μe conversion as well as flavour-violating KL decays should occur at levels close to present experimental limits if dynamical symmetry breaking as envisaged by technicolour theories is indeed realised in nature.