Minimal subconstituent models of quarks and leptons

We analyze the structure of composite quarks and leptons in the framework of chiral subconstituent models of minimal internal symmetry. The model of Harari and Shupe contains the correct number of composite fields but it cannot sustain an exact color symmetry. An extension of the Harari-Shupe model is proposed, with both color and electromagnetic properties being realized linearly on the subconstituents. This model contains two generations of quarks and leptons; all models of this type contain additional quarklike states or leptonlike states of higher spin. Problems associated with the implementation of the approximate weak-electromagnetic symmetry and with the statistics of subconstituents are discussed.