Intuitive

The flavor puzzle is the question why do the particles in the standard model of particle physics have the values they have, and why do the mixing angles in the PMNS and CKM matrix have the values they have.

Concrete

• The Fermion Mass Problem by K.S. Babu
• A Model-Building Approach to the Origin of Flavor by E. Schuhmacher
• Pieces of the Flavour Puzzle by Ferruccio Feruglio

Abstract

Research

The Yukawa couplings express the flavour problem, i.e. our inability to compute quark and lepton masses and mixing angles. […]

no significant progress has ever been made in computing quark and lepton masses and mixing angles or understanding the dynamical origin of their pattern. […] Given our failure in cracking the flavour problem, it is unlikely that its solution is simple and that it manifests itself in simple ways. Only crazy results in flavour physics have a chance to be true.

https://arxiv.org/pdf/1710.07663.pdf#page23

Flavor Democracy

See Flavor Democracy

"all fermions are created equal"

See On the proposition that all fermions are created equal by Howard Georgi, Ann Nelson, Aneesh Manohar

Flavor Symmetries

For a great introduction, see this thesis.

Why is it interesting?

"In a recent interview published in CERN COURIER, Steven Weinberg was asked what single open question he would like to see answered in his lifetime, and Weinberg replied that it is only the mystery of the observed pattern of quark and lepton masses[1]. " https://arxiv.org/pdf/1712.08052.pdf