It has been proposed that the quarks and leptons consist of more fundamental particles called rishons. The T rishon may be defined as having mass and charge e/3. The V rishon is neutral and has little or no mass. The rishons have spin 1/2, carry color charge, and combine in triplets or rishon-antirishon pairs. Thus the electron is a TTT, the neutrino VVV, the down quark TVV, and the up quark TTV. If the T has somewhat greater color charge than the V, the down quark would have a net excess of the color carried by the T. The antiup quark TTV would appear to have a net deficiency of the color carried by the V, or equivalently, an excess of anticolor, and behave as an antiparticle. Hence the TTV would appear to have an excess of color and behave as a particle, in agreement with observation. The leptons have no net color. There is no need for hypercolor.

All particle interactions consist of rearrangements of rishons, or creation or annihilation of rishon-antirishon pairs. For example, beta-decay occurs when a down quark changes to an up quark, emitting an electron and neutrino:

TVV --> TTV + TTT + VVV

The massless particle was originally called a neutrino; it was later defined to be an antineutrino. This model favors the first choice.

If the binding between rishons is much greater than the binding between quarks or leptons, then quarks and leptons could associate without losing their identity, just as atoms can form molecules. Lepton number is also conserved if the VVV is assigned a negative lepton number.

The second and third generations of the electron and the quarks might be formed by adding one or two TT pairs to the first generation. The second and third generations of the neutrino might be formed by adding one or two VV pairs to the first generation. The force binding the rishons is evidently so great that the separate rishon wave functions 'fall' together into just one wave function, in which case there would be no internal structure.

The effective mass of the TTV is nearly equal to that of the TVV, which implies that the T-T bond has binding energy nearly equal to the bare mass of a T. The electron has three T's and three bonds and hence should have little mass compared to a quark, as observed. The muon obtains most of its mass from the added TT and should have a mass comparable to that of a quark, as observed.

The boson carriers of the weak force presumably consist of the rishons required to form the decay products. The photon may consist of a colorless VV pair; for example red-antired. The gluon may consist of a colored VV pair, for example red-antiblue. Hence the weak force may simply be the color force carried by weak bosons; the electromagnetic force is the color force carried by photons, and the strong force is the color force carried by gluons, mesons, quarks, and possibly other hadrons.

A real TT would annihilate, while a virtual pair might help carry the strong force. A bare rishon, a TV, TV, TT, or VV would carry net color and, like the quarks, would not be seen in isolation.

The proton consists of two up quarks and a down quark, so the hydrogen atom has four T's, four T's, two V's, and two V's. If this typifies the whole universe, then there exist equal amounts of rishons and antirishons.

One might speculate further that the emission and absorption of virtual particles is just Hawking radiation. The spacetime itself around a rishon might have quantum states. The large spin of a rishon would eliminate the spherically symmetric S states, leaving three P states with the time coordinate expanded, and three P states with the time coordinate compressed. These might be identified with the three colors and three anticolors. The difference in the time coordinate would cause a slight difference in the reaction rates of rishons and antirishons, explaining why hydrogen is more abundant than antihydrogen. Another possibility is that the rishons and antirishons have opposite handedness and parity violation causes a difference in the reaction rates. The rishons themselves may be just quanta of spacetime. The V rishon might be the lowest P state, and the T rishon the next-highest P state. Thus the T and V would be similar, but somewhat mismatched, as observed.

If this sort of model is correct, it would be the basis of the long-sought unified field theory. The strong, weak, and electromagnetic forces are just the color force carried by intermediates, and the color force itself may be identified with quantum gravity of which ordinary gravity is the long-range limit.

Reference

Haim Harari, "The Structure of Quarks and Leptons," Scientific American, p.56, April 1983.