$S^\prime_4$ Quark Flavour Model in the Vicinity of the Fixed Point $\tau = i\infty$

Abstract

We study in the bottom-up framework the possibility to generate the quark mass hierarchies without fine-tuning, the quark mixing and CP-violation (CPV) in a flavour model with $S^\prime_4$ modular symmetry having minimal number of parameters. The model is considered in the vicinity of the fixed point $\tau_\text{T}= i\infty$, $\tau_\text{vev} \sim \tau_\text{T}$, $\tau_\text{vev}$ being the vacuum expectation value (VEV) of the modulus $\tau$, which allows to explain the hierarchies of the quark masses. The ten quark observables are described by nine real parameters. The CP-symmetry is broken explicitly since, as is well known, reproducing the observed CPV in the quark sector in the case of spontaneous breaking of CP-symmetry by $\tau_\text{vev}$ is highly problematic in the class of minimal modular quark flavour models (explaining the quark mass hierarchies without fine-tuning) of the type we consider. We perform a statistical analysis of the model and show that it is phenomenologically viable and consistent, in particular, with the ``inclusive'' decay data on the $|V_{ub}|$ and $|V_{cb}|$ elements of the CKM matrix and, in the case of a very high scale of supersymmetry breaking, with the current ``average'' experimental values of $|V_{ub}|$ and $|V_{cb}|$.