E6model with composite muon andτfamilies

We present a unified model based on the exceptional group ${\mathrm{E}}_6$ in which the electron family ($e$,${\nu }_e$,$u$, and $d^{\prime }$, where the prime denotes a Cabibbo-rotated state) is elementary, and the $\mu$ and $\tau$ families are composites. The model has a rich particle spectrum starting not far above the $\tau$ family and a range of mass scales above the weak-boson masses. Group-theoretical features of the symmetry breaking are discussed in some detail in a language having many other applications.