David Morin

Effects of top quark compositeness

We investigate the effects of top quark compositeness on various physical parameters, and obtain lower limits on the compositeness scale from electroweak precision data. We consider corrections to top quark decay rates and other physical processes. Our results depend sensitively on whether the left-handed top quark is composite. A considerable enhancement of [ital t[bar t]] production is possible if only the right-handed top quark is composite.

Decays of l = 1 baryons: Quark model versus large N(c)

We study nonleptonic decays of the orbitally excited, SU(6) 70-plet baryons in order to test the hypothesis that the successes of the nonrelativistic quark model have a natural explanation in the large-Nc limit of

Nonperturbative matching for field theories with heavy fermions.

We examine a paradox, suggested by Banks and Dabholkar, concerning nonperturbative effects in an effective field theory which is obtained by integrating out a generation of heavy fermions, where the heavy fermion masses arise from Yukawa couplings. They argue that light fermions in the effective theory appear to decay via instanton processes, whereas their decay is forbidden in the full theory. We resolve this paradox by showing that such processes in fact do not occur in the effective theory, due to matching corrections which cause the relevant light field configurations to have infinite action.