Renormalization Group Equations for the CKM matrix

TL;DR

This paper derives one-loop renormalization group equations for the CKM matrix in various models, revealing invariants like the unitarity triangle angle and showing certain shape parameters are conserved across energy scales.

Contribution

It introduces a novel derivation method for the RG equations of the CKM matrix and identifies invariants such as the unitarity triangle angle across different models.

Findings

The unitarity triangle angle α is invariant under RG evolution.

The shape of the unitarity triangle and Buras-Wolfenstein parameters are conserved for certain model conditions.

CKM matrix's special forms cannot be achieved at asymptotic energies.

Abstract

We derive the one loop renormalization group equations for the Cabibbo-Kobayashi-Maskawa matrix for the Standard Model, its two Higgs extension and the minimal supersymmetric extension in a novel way. The derived equations depend only on a subset of the model parameters of the renormalization group equations for the quark Yukawa couplings so the CKM matrix evolution cannot fully test the renormalization group evolution of the quark Yukawa couplings. From the derived equations we obtain the invariant of the renormalization group evolution for three models which is the angle $\alpha$ of the unitarity triangle. For the special case of the Standard Model and its extensions with $v_{1}\approx v_{2}$ we demonstrate that also the shape of the unitarity triangle and the Buras-Wolfenstein parameters $\bar{\rho}=(1-{1/2}\lambda^{2})\rho$ and $\bar{\eta}=(1-{1/2}\lambda^{2})\eta$ are conserved. The invariance of the angles of the unitarity triangle means that it is not possible to find a model in which the CKM matrix might have a simple, special form at asymptotic energies.