A separate SU(2) for the third family: Topflavor
  We consider an extended gauge group for the electroweak interaction: SU(2)_1 \times SU(2)_2 \times U(1)_Y where the first and second generations of fermions couple to SU(2)_1 while the third generation couples to SU(2)_2. Bounds based on precision observables and heavy gauge boson searchesare placed on the new parameters of the theory, and the potential of the theory to explain R_b and R_c is explored. We investigate processes that could produce observable signals at the LHC and NLC. 
David Muller and Satya Nandi