New Topflavor Models with Seesaw Mechanism

New class of models are constructed in which the third family quarks, but not leptons, experience a new SU(2) or U(1) gauge force. Anomaly cancellation enforces the introduction of spectator quarks so that the top and bottom masses are naturally generated via a seesaw mechanism. We find the new contributions to the (S,T,U) parameters and Zbb vertex to be generically small. We further analyze how the reasonable flavor-mixing pattern can be generated to ensure the top-seesaw mechanism and sufficiently suppress the flavor-changing effects for light quarks. Collider signatures for the light Higgs boson and top quark are also discussed.