Rare top quark and Higgs boson decays in alternative left-right symmetric models

Top quark and Higgs boson decays induced by flavor-changing neutral currents (FCNC) are very much suppressed in the standard model. Their detection in colliders such as the Large Hadron Collider, Next Linear Collider, or Tevatron would be a signal of new physics. We evaluate the FCNC decays t{yields}H{sup 0}+c, t{yields}Z+c, and H{sup 0}{yields}t+c in the context of alternative left-right symmetric models with extra isosinglet heavy fermions; in this case, FCNC decays occur at tree level, and they are suppressed only by the mixing between ordinary top and charm quarks, which is poorly constrained by current experimental values. This provides the possibility for future colliders either to detect new physics or to improve present bounds on the parameters of the model.