Origin of Fermion Identity and the Yukawa Hierarchy

Determine the dynamical mechanism that sets the identities of fermions—specifically, establish the origin and scale of the Yukawa couplings that distinguish the electron from the top quark and yield the observed hierarchy of fermion masses and mixings in the Standard Model.

Background

The paper notes that at least twenty of the Standard Model’s parameters pertain to flavor (masses and mixings), yet no theory currently explains their values or organizing principles. Even if the Higgs mechanism generates masses, the reasons for the numerical patterns remain unknown.

Understanding the mechanism behind fermion identity would address a central gap in the Standard Model, with implications for unification, CP violation, and possible new symmetries or dynamics.

References

We do not know, for example, what makes an electron an electron and a top quark a top quark.

— Perspectives and Questions: Toward an Expansive Agenda for Particle Physics  (2510.06348 - Quigg, 7 Oct 2025) in Section 5, Flavor I: the Problem of Identity

Separating the four families into distinct flavours remains an open problem, taken up again in Sec.~\ref{sec6}.

— Conformal and Noncommutative Gravity from Gauge Symmetry Breaking and SO(2,16) Unification  (2608.23220 - Stefas et al., 24 Aug 2026) in Section 4, final paragraph before Section 6; reiterated in Section 6