Minimal Solutions to the CKM Unitarity Problem with a Vector-like Quark Isosinglet

José Filipe Bastos

Key information

Authors:

José Filipe Bastos (José Filipe Bastos)

Supervisors:

Joaquim Inácio da Silva Marcos (Joaquim Inácio da Silva Marcos)

Published in

February 3, 2022

Abstract

Recent results and calculations provide strong evidence that the CKM matrix is not unitary, contradicting the Standard Model (SM) and suggesting New Physics (NP). In this thesis, we propose a minimal extension of the SM where an up-type vector-like quark isosinglet, denoted by T, is introduced, leading to a simple solution to the CKM unitarity problem (CKM-UP). We adopt the Botella-Chau parametrization for the 4×3 quark mixing-matrix, containing the usual three angles and phase of the 3×3 SM-mixing, plus three extra angles s_14,s_24,s_34 and two phases δ_14,δ_24. To fully achieve a minimal solution to the CKM-UP, we assume that the mixing of T with standard quarks is dominated by s_14. Interesting features and a novel pattern of T decays, predominantly to the first generation, are obtained. However, one has to make sure that the limits of Electroweak Precision Measurements (EWPM) from experiment, are not exceeded. We have found that ε_K, sensitive to CP violation, plays a crucial role in constraining these type of models. Imposing a (recently derived) restrictive upper-bound on NP to ε_K, we find, in the limit of exact s_14-dominance where s_24,s_34=0, that ε_K^NP is too large. If, however, one relaxes this exact s_14-dominance limit, a significantly large parameter region is obtained, where ε_K^NP is in agreement with experiment, maintaining previously encountered features. Other important EWPM associated quantities are also studied. To a good approximation, these results are independent of s_34, allowing for solutions solely using three NP parameters: s_14,s_24 and δ'=δ_24-δ_14.