Bottom-Up Discrete Symmetries for Cabibbo Mixing

TL;DR

This paper investigates discrete non-Abelian symmetries to explain the Cabibbo angle in quark mixing, using a bottom-up approach and computational group theory to identify finite groups capable of quantizing this parameter.

Contribution

It introduces a method to construct and discretize residual symmetry generators for the CKM matrix, highlighting limitations of small finite groups in predicting all mixing parameters.

Findings

Small finite groups of order around 100 cannot predict all CKM parameters.

Discretization of degrees of freedom enables the use of GAP to identify finite symmetry groups.

Natural flavor models may need to incorporate smaller groups with additional correction mechanisms.

Abstract

We perform a bottom-up search for discrete non-Abelian symmetries capable of quantizing the Cabibbo angle that parameterizes CKM mixing. Given a particular Abelian symmetry structure in the up and down sectors, we construct representations of the associated residual generators which explicitly depend on the degrees of freedom present in our effective mixing matrix. We then discretize those degrees of freedom and utilize the Groups, Algorithms, Programming (GAP) package to close the associated finite groups. This short study is performed in the context of recent results indicating that, without resorting to special model-dependent corrections, no small-order finite group can simultaneously predict all four parameters of the three-generation CKM matrix and that only groups of $\mathcal{O}(10^{2})$ can predict the analogous parameters of the leptonic PMNS matrix, regardless of whether neutrinos are Dirac or Majorana particles. Therefore a natural model of flavour might instead incorporate small(er) finite groups whose predictions for fermionic mixing are corrected via other mechanisms.