The Harari–Shupe preon model (also known as rishon model, RM) is the earliest effort to develop a preon model to explain the phenomena appearing in the Standard Model (SM) of particle physics. It was first developed by Haim Harari and Michael A. Shupe (independently of each other), and later expanded by Harari and his then-student Nathan Seiberg.
The model has two kinds of fundamental particles called rishons (which means "primary" in Hebrew). They are T ("Third" since it has an electric charge of ⅓ e, or Tohu which means "unformed" in Hebrew Genesis) and V ("Vanishes", since it is electrically neutral, or Vohu which means "void" in Hebrew Genesis). All leptons and all flavours of quarks are three-rishon ordered triplets. These groups of three rishons have spin-½. They are as follows:
- TTT = antielectron;
- VVV = electron neutrino;
- TTV, TVT and VTT = three colours of up quarks;
- TVV, VTV and VVT = three colours of down antiquarks.
Each rishon has a corresponding antiparticle. Hence:
- TTT = electron;
- VVV = electron antineutrino;
- TTV, TVT, VTT = three colours of up antiquarks;
- TVV, VTV, VVT = three colours of down quarks.
Baryon number (B) and lepton number (L) are not conserved, but the quantity B−L is conserved. A baryon number violating process (such as proton decay) in the model would be
u + u → d + e+
/|\ /|\ /|\ /|\
TTV + TTV → TVV + TTT
- Matter and antimatter are equally abundant in nature in the RM.
- Higher generation leptons and quarks are presumed to be excited states of first generation leptons and quarks.
- Mass is not explained.
In the expanded Harari–Seiberg version  the rishons possess color and hypercolor, explaining why the only composites are the observed quarks and leptons. Under certain assumptions, it is possible to show that the model allows exactly for three generations of quarks and leptons.
Currently, there is no scientific evidence for the existence of substructure within quarks and leptons, but there is no profound reason why such a substructure may not be revealed at shorter distances. In 2008, Piotr Zenczykowski has derived the RM by starting from a non-relativistic O(6) phase space. Such model is based on fundamental principles and the structure of Clifford algebras, and fully recovers the RM by naturally explaining several obscure and otherwise artificial features of the original model.
In popular culture
- Science fiction author Vonda McIntyre, in her novelizations of the scripts of the movies Star Trek II: The Wrath of Khan and Star Trek III: The Search for Spock suggested that the Genesis effect was a result of a newly discovered rishon-like substructure to matter.
- Science fiction author James P. Hogan in his novel Voyage from Yesteryear explicitly postulated a rishon-like model in the development of antimatter weapons and energy sources.
- Harari, H. (1979). "A Schematic Model of Quarks and Leptons". Physics Letters B 86 (1): 83–86. Bibcode:1979PhLB...86...83H. doi:10.1016/0370-2693(79)90626-9.
- Shupe, M. A. (1979). "A Composite Model of Leptons and Quarks". Physics Letters B 86 (1): 87–92. Bibcode:1979PhLB...86...87S. doi:10.1016/0370-2693(79)90627-0.
- Zenczykowski, P. (2008). "The Harari–Shupe preon model and nonrelativistic quantum phase space". Physics Letters B 660 (5): 567–572. arXiv:0803.0223. Bibcode:2008PhLB..660..567Z. doi:10.1016/j.physletb.2008.01.045.