A new review paper which will be a chapter in an Encyclopedia of Particle Physics summarizes various theories that have been advanced to explain the fundamental fermion masses in the Standard Model, and while it isn't complete, its table of contents is a nice summary of some of the leading approaches.
2 Fermion masses and mixing angles
2.1 The Standard Model2.2 Neutrino masses
Majorana neutrino massesThe seesaw mechanismType-I seesaw
Type-III seesawType-II seesawDirac neutrino mass
2.3 The data
3 In search of an organizing principle4 Grand Unified Theories
4.1 SU(5) GUTs4.2 SU(10) GUTs
5 Fermion masses from quantum corrections
5.1 Radiative fermion masses5.2 Infrared fixed points
6 CompositeFermions
6.1 Massless composite fermions6.2 Partial compositeness
7 Flavor Symmetries
7.1 The Froggatt-Nielsen Model7.2 Variants and alternatives
8 Fermion masses in String Theory
8.1 Aiming at the SM from strings8.2 Eclectic flavor symmetries from heterotic orbifolds8.3 Flavor in models with D-branes8.4 Metaplectic flavor symmetries from magnetized branes
The LP & C relationship, and the kind of dynamical balancing rules that I favor don't get a mention, although they come closest to the quantum corrections approach.
what Theories To Explain The Fundamental Fermion Masses do you back up the most ?
ReplyDeleteString Theory and SU(5) GUTs are DOA. There is strong experimental evidence disfavoring composite fermions. The evidence that underlies the Froggatt-Nielsen model is interesting but hasn't produced much fruit. I doubt that an SU(10) GUT will work, but it is harder to definitively rule out. Quantum corrections is potentially a fruitful general approach, but efforts to develop it so far haven't gotten very far. I don't have an answer of my own for the neutrino masses, but I think that they are not Majorana fermions and that the seesaw mechanism is not correct
ReplyDeletewhat about yukawa coupling to Higgs field
ReplyDelete@neo That's basically what Dirac mass is. We'd never see it in Higgs decays because the coupling would be so weak. The lack of a right handed neutrino, and the lack of a left handed anti-neutrino throws a wrench in the conventionally formulated Higgs mechanism. I think that neutrino mass primarily arising from W and Z boson interactions is more likely (and of course, the W and Z bosons obtain their masses via the Higgs mechanism, so this would be basically an indirect Higgs mechanism model, possibly helping to explain why neutrino masses are so small). Notably, the ratio of charged lepton masses to neutrino masses is of the same order of magnitude as the ratio of the electromagnetic force strength to the weak force strength, which is notable because charged leptons interact via both, while neutrinos interact only via the weak force.
ReplyDeleteThe quarks and charged leptons and W, Z, and Higgs bosons all do get their masses via their couplings to the Higgs field. But that begs the question of why we have the particular twelve Yukawa couplings to the Higgs field that we observe, which have a definite structure including LP&C and Koide's rule, and something close to Koide's rule for quarks, and the 2 H = Z + 2W + zero photon mass relation which holds approximately to less than 2% and could be explained as a bosonic superposition with quantum corrections.
My intuition is that the Higgs vev (which is a function of the weak force coupling constant) sets the mass-scale for the Higgs mechanism overall, and that the quark and charged lepton masses are a result of dynamic balancing of the Yukawas via W boson interactions in accordance with the CKM matrix which is more fundamental than the Higgs Yukawas, according to a generalized Koide's rule that is simpler for charged leptons because of lepton universality and their identical electromagnetic charges, probably because the neutrino masses are so negligible that they virtually zero out terms in a generalized Koide's rule relationship.