preonic

Preon is a hypothetical subcomponent proposed to be the fundamental building block of quarks and leptons. Emerging in the 1970s, preon models aim to explain patterns among fermions, charge quantization, and family replication by treating quarks and leptons as bound states of a small set of more elementary constituents. The best-known scheme is the rishon model, which posits two basic preons whose three-preon composites form the observed particles. Other approaches include Harari–Shraiman models and related constructions. These theories typically require a new binding interaction or gauge force to confine preons at very high energy scales.

Predicted consequences include non-pointlike behavior at high momentum transfers, excited fermion states, and new contact interactions among Standard Model particles. Experimental searches for substructure—through deviations in scattering and limits on compositeness scales—have found no evidence of preons. Deep inelastic scattering experiments and collider data from HERA and the LHC push lower bounds on the compositeness scale into the multi-TeV range, depending on the model. Theoretical challenges, including issues of chirality, anomaly cancellation, and proton stability in many constructions, have limited viable preon models.

Today, preon ideas remain speculative and are not part of the established Standard Model. They are discussed within broader beyond-Standard Model research, especially in approaches emphasizing compositeness, extra dimensions, or string-inspired substructure. While some models persist in theoretical work, the lack of experimental confirmation maintains preons as an exploratory concept rather than a validated description of matter's substructure.