Two Higgs doublets with 4th generation fermions - models for TeV-scale   compositeness
  We construct a class of two Higgs doublets models with a 4th sequential generation of fermions that may effectively accommodate the low energy characteristics and phenomenology of a dynamical electroweak symmetry breaking scenario which is triggered by the condensates of the 4th family fermions. In particular, we single out the heavy quarks by coupling the "heavier" Higgs doublet (\Phi_h) which possesses a much larger VEV only to them while the "lighter" doublet (\Phi_l) couples only to the light fermions. We study the constraints on these models from precision electroweak data as well as from flavor data. We also discuss some distinct new features that have direct consequences on the production and decays of the 4th family quarks and leptons in high energy colliders; in particular the conventional search strategies for t' and b' may need to be significantly revised. 
Shaouly Bar-Shalom, Soumitra Nandi, Amarjit Soni
hep-ph hep-ex