Decays of the heavy top and new insights on epsilon _K in a one-VLQ minimal solution to the CKM unitarity problem

Abstract

We propose a minimal extension of the Standard Model where an up-type vector-like quark, denoted T, is introduced and provides a simple solution to the CKM unitarity problem. We adopt the Botella-Chau parametrization in order to extract the 4times 3 quark mixing matrix which contains the three angles of the 3times 3 CKM matrix plus three new angles denoted theta _{14}, theta _{24}, theta _{34}. It is assumed that the mixing of T with standard quarks is dominated by theta _{14}. Imposing a recently derived, and much more restrictive, upper-bound on the New Physics contributions to epsilon _{K}, we find, in the limit of exact theta _{14} dominance where the other extra angles vanish, that epsilon _{K}^{text {NP}} is too large. However, if one relaxes the exact theta _{14} dominance limit, there exists a parameter region, where one may obtain epsilon _{K}^{text {NP}} in agreement with experiment while maintaining the novel pattern of T decays with the heavy quark decaying predominantly to the light quarks d and u. We also find a reduction in the decay rate of K_Lrightarrow pi ^0 nu {overline{nu }}.