Towards understanding fermion masses and mixings

TL;DR

This paper investigates fermion mass hierarchies and mixing patterns, proposing a modified Fritzsch texture compatible with current data and exploring theoretical models like $SU(5)$ with $SU(3)_H$ symmetry.

Contribution

It introduces a minimal modification to Fritzsch's Yukawa matrix ansatz, aligning it with experimental data and providing a theoretical framework within $SU(5)$ models.

Findings

Modified Fritzsch texture fits current quark data

Asymmetry in Yukawa matrix entries is compatible with observations

Theoretical realization within $SU(5)$ with $SU(3)_H$ symmetry

Abstract

The Standard Model does not constrain the form of the Yukawa matrices and thus the origin of fermion mass hierarchies and mixing pattern remains puzzling. On the other hand, there are intriguing relations between the quark masses and their weak mixing angles, such as the well-known one $\tan \theta_C= \sqrt{m_d/m_s}$ for the Cabibbo angle, which may point towards specific textures of Yukawa matrices hypothesized by Harald Fritzsch at the end of the 70's. Though the original ansatz of Fritzsch is excluded by the experimental data, one can consider its minimal modification which consists in introducing an asymmetry between the 23 and 32 entries in the down-quark Yukawa matrix. We show that this structure is perfectly compatible with the present precision data on quark masses and CKM mixing matrix, and theoretically it can be obtained in the context of $SU(5)$ model with inter-family $SU(3)_H$ symmetry. We also discuss some alternative approaches which could give a natural description of the fermion mass spectrum and weak mixing pattern.