Signals from flavor changing scalar interactions in extended models

If on the one hand many predictions of the Standard Model seem to be in remarkable agreement with experiments, on the other hand the full consistency of the model needs still to be proved. In particular, given our present ignorance of the Higgs sector of the theory, extensions of the Standard Model scalar sector are worth considering. The simplest extension of adding one extra SU(2) doublet of scalar fields, i.e. the Two Higgs Doublet Model, generally introduces Flavor Changing Scalar Neutral Currents. The severe constraints imposed by the low energy physics of K and B mesons (K0 - bar K0 and B0 - bar B0 mixing in particular) have motivated the introduction of an unnatural discrete symmetry to avoid flavor changing scalar neutral currents. This assumption may be dropped in favor of a more natural one, which takes any flavor changing coupling to be proportional to the mass of the coupled quarks. The basic idea is that a natural hierarchy is provided by the observed fermion masses and this may be transferred to the couplings between fermions and scalar fields, even when they are not the ones directly involved in the mass generation mechanism. This report presents a Yukawa lagrangian that incorporates this assumption and describes experimental consequences, involving production of top and charm quark pairs, that would serve to test it. 9 refs., 2 figs