What determines the hierarchy of quark and lepton masses? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
What determines the hierarchy of quark and lepton masses?
Plain
The top quark is about 340000 times heavier than the electron, and quark mixing is small while neutrino mixing is large. No theory predicts these numbers.
Precise · changed · core
Revision 1: The SM Yukawa couplings span $y_e \sim 3e-6$ to $y_t \sim 1$, CKM angles are small ($\theta_C \sim 0.23$, |V_ub| ~ 4e-3) while PMNS angles are large ($\theta_{12} \sim 34\,\mathrm{deg}$, $\theta_{23} \sim 45\,\mathrm{deg}$). An answer is a mechanism (Froggatt-Nielsen charges, modular or discrete flavor symmetries, extra-dimensional localization, partial compositeness) that predicts these values with fewer parameters than it explains.
Revision 2: The SM Yukawa couplings span $y_e \sim 3 \times 10^{-6}$ to $y_t \sim 1$, CKM angles are small ($\theta_C \sim 0.23$, $\mid V_{ub}\mid$ $\sim 4 \times 10^{-3}$) while PMNS angles are large ($\theta_{12} \sim 34\,\mathrm{deg}$, $\theta_{23} \sim 45\,\mathrm{deg}$). An answer is a mechanism (Froggatt-Nielsen charges, modular or discrete flavor symmetries, extra-dimensional localization, partial compositeness) that predicts these values with fewer parameters than it explains.
Settled by
A model with fewer free parameters than observables whose extra predictions (mixing sum rules, flavor-violating rates, new states) are confirmed.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
open
Status note
(empty)
Posed since
(empty)

Decisions