Mass Bounds in Mirror-Fermion Models

Numerical simulations are performed on different lattice sizes of chiral U(1) and SU(2) scalar-fermion models with explicit mirror pairs of fermions in the broken symmetry phase. Relevance of these models to the electroweak theory is discussed. Shift symmetry of the action is exploited to decouple the unwanted mirror-fermion. Upper and lower bounds on the renormalized scalar mass as a function of the renormalized fermion mass are obtained in the SU(2) version of the model. Our numerical data are found to be in qualitative agreement with one-loop results. No evidence for a nontrivial fixed point has been observed. The mirror-fermion models are likely to be trivial in the continuum limit. Our Monte Carlo data show that with a 180GeV top quark, the Standard Model Higgs boson should have a mass between 100 and 800GeV .