Nondecoupling of a terascale isosinglet quark and rare K and B decays

TL;DR

This paper investigates how a heavy isosinglet T quark, predicted by certain extensions of the standard model, can influence rare K and B meson decays through nondecoupling effects, potentially detectable at the LHC.

Contribution

It demonstrates the nondecoupling effects of a terascale isosinglet T quark on rare meson decays and shows these effects are largely independent of the T quark mass.

Findings

Residual effects can increase decay rates by up to 50%.

Maximal decay rate corrections are roughly 20-30%.

Nondecoupling effects are largely independent of T quark mass.

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.