Bounds on the renormalized couplings in an SU(2)_L otimes SU(2)_R symmetric Yukawa model

The vacuum stability lower bound on the mass of the Higgs boson is numerically investigated in an $SU(2)_L \otimes SU(2)_R$ symmetric Yukawa model, which describes two heavy degenerate fermion doublets in the limit of vanishing gauge couplings. Good agreement with perturbation theory is found, although the couplings are strong. The upper bound on the fermion mass and renormalized Yukawa coupling is also determined in the part of bare parameter space where reflection positivity has been proven.