Origin of flavor hierarchies

Explain the origin of the observed flavor hierarchies in the Standard Model, including the patterns of fermion masses and mixing angles across quarks and leptons.

Background

The introduction highlights the flavor puzzle—why fermion masses and mixings span many orders of magnitude—as a central unresolved issue in the Standard Model.

The paper’s focus on muon-specific interactions and precision kinematics at a muon collider is motivated partly by the potential to uncover new flavor structures, such as muon-philic interactions, that could shed light on flavor hierarchies.

References

Among these are the apparent unnaturalness of the electroweak scale, the particle nature of dark matter (DM), and the origin of the observed flavor hierarchies. These open problems suggest the existence of new physics beyond the SM (BSM) and have motivated extensive theoretical and experimental efforts to uncover it.

— On the Run from the Dark Side of the Muon  (2602.16771 - Asadi et al., 18 Feb 2026) in Section 1 (Introduction)

An open question that the Standard Model (SM) has not been able to answer concerns its flavor structure.

— Quark Mixing Model with Three Higgs Doublets and $S_3$ Modular Symmetry at $τ=i$  (2609.03204 - Cerón et al., 2 Sep 2026) in Section 1, Introduction

The origin of fermion mass hierarchies and mixing remains an open problem in particle physics.

— The Flavor of Non-Abelian Orbifolds  (2609.30241 - Hernandez-Segura et al., 24 Sep 2026) in Section 1, Introduction

The first relation is probably not so useful, as we do not know the structure of $\mathbf{Y}_\nu$.

— Constructing $SU(N)$ strongly coupled dark sectors by extending the Standard Model: mixed representations, flavor structure, global symmetries and various portals  (2610.12040 - Chung, 8 Oct 2026) in Section 2.3, subsection Lepton Portal