Prishon said:
The
risbon model model was inveted by Harari in 1981. It is a theory that lies beyond the standard model and explains the existence of quarks and leptons on the basis of jusr 2 elementary particles, the T- and V-rishon (heuristically that is, like the quark model did once for the plethora of hadrons and mesons).
But what are its drawbacks? Apart from the trivial answer that it is not proven. Though the muon g2 is a strong hint that the muon consists of three anti T-rishons (and for example, the up quark consists of two T-rishons and one V-rishon). The mass of the neutrino is another hint of compositeness (together with the seesaw mechanism, another possibility to account for neutrino mass).
The main problems are that experimental data is so far inconsistent with a composite nature for quarks and leptons up to a very high energy scale (24 TeV or more by the most strict exclusion), and with very low electric (as opposed to magnetic) dipole moments (consistent with zero) of quarks and
leptons. The rishon model also doesn't account for the fact that we observe three generations of Standard model fermions. The
experimental bounds in quark and lepton compositeness are summarized at the Particle Data Group. These limits are explained in
a related review article.
See also the discussions of experimental barriers including the mass paradox in this
discussion of preons more generally. In a nutshell, the Heisenberg uncertainty principle would indicate uncertainty in the fundamental particle masses much greater than observed if indeed they were composite particles that are at least as small as experimental observations require.
Also, muon g-2 proves no such thing. Indeed, there are two completing theoretical calculations of muon g-2's expected value, one of which incorporates more experimental measurements, and the other of which is more fully from first principles calculations by the
BMW group, and the later is perfectly consistent with the experimental measurements of muon g-2 which would suggest that there is no muon g-2 anomaly to explain.
Further, to the best of my knowledge, there have been no efforts to describe a rishon model in terms of muon g-2 or composite leptons.
The mass of the neutrino is strong evidence that the pre-massive neutrino Standard Model was missing something. It is not evidence of compositeness in particular. None of the leading theories seeking to explain the source of neutrino mass resort to a composite neutrino model.
