Precision constraints on extra fermion generations

Phys Rev Lett. 2010 Jul 16;105(3):031801. doi: 10.1103/PhysRevLett.105.031801. Epub 2010 Jul 13.

Abstract

There has been recent renewed interest in the possibility of additional fermion generations. At the same time there have been significant changes in the relevant electroweak precision constraints, in particular, in the interpretation of several of the low energy experiments. We summarize the various motivations for extra families and analyze them in view of the latest electroweak precision data.