Nondecoupling of a terascale isosinglet quark and rare K and B decays
Abstract
We examine recent extensions of the standard model with an up-type vectorlike isosinglet T quark that mixes dominantly with the top quark. We take under scrutiny the nondecoupling effects which may reveal such a new heavy fermion through loop diagrams relevant for rare decays such as K-->pi nu nu-bar, B-->pi(K) nu nu-bar, and Bs,d-->mu+ mu-. After demonstrating in detail the cancellation between the leading nondecoupling terms, we show that two residual forms ~ s2 lnmT2 and ~ s4 mT2 act in complementary way, so that the maximal allowed values of the decay rates are practically independent of mT. While they correspond to ~ 20% or ~ 30% corrections to the SM rates for K-->pi nu nu-bar and B-->pi(K) nu nu-bar, an increase by ~ 50% for Bs,d-->mu+ mu- decays offers a possibility to reveal an additional isosinglet state by measurements of these decays at the Large Hadron Collider.