Evading the top-quark mass bound at the Fermilab Tevatron: New signals for the top quark

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Abstract
If an SU(2)-singlet charge-2/3 quark exists, current data allow a wide range for the parameters of the 4×4 mixing matrix in which the usual ‘‘hard-lepton’’ signal of the top quark is suppressed. For a light Higgs boson, the top quark decays predominantly via the flavor-changing Yukawa interaction, thus evading the Fermilab Tevatron bounds on its mass. For a heavier Higgs boson, flavor-changing neutral-current decays become important, giving rise to anomalous Z-pair production, testable at the upgraded Tevetron, at the CERN Large Hardon Collider, and at the Superconducting Super Collider.