Gauged baryon and lepton numbers

A possible extension of the standard model can be defined by gauging the global baryon- and lepton-number U(1) symmetries. Gauging baryon and lepton numbers provides a natural framework for the seesaw mechanism in the lepton sector, and the Peccei-Quinn mechanism in the quark sector. Another consequence of this extension is that the usual three generations of fermions are not anomaly-free. However, we consider a wider framework involving the existence of generations with exotic SU(2)LU(1)Y quantum numbers. This allows us to "derive" a spectrum of fermions which contain the known quarks and leptons.