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 B_{s,d}-->mu^+ mu^-. After demonstrating in detail the cancellation between the leading nondecoupling terms, we show that two residual forms ~ s^2 ln{m_T^2} and ~ s^4 m_T^2 act in complementary way, so that the maximal allowed values of the decay rates are practically independent of m_T. 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 B_{s,d}-->mu^+ mu^- decays offers a possibility to reveal an additional isosinglet state by measurements of these decays at the Large Hadron Collider.

17 pages, 6 figures, LaTeX, matches published version

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• Small violations of unitarity, the phase in Bs mixing and visible t->cZ decays at the LHC
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• Decays of the Heavy Top and New Insights on ${\epsilon }_K$ in a one-VLQ Minimal Solution to the CKM Unitarity Problem
• Singlet Heavy Fermions as the Origin of B Anomalies in Flavour Changing Neutral Currents