An exploratory numerical study of the influence of heavy fermion doublets on
the mass of the Higgs boson is performed in the decoupling limit of a chiral
SU(2)L⊗SU(2)R symmetric Yukawa model with mirror fermions. The
behaviour of fermion and boson masses is investigated at infinite bare quartic
coupling on 43⋅8, 63⋅12 and 83⋅16 lattices. A first
estimate of the upper bound on the renormalized quartic coupling as a function
of the renormalized Yukawa-coupling is given.Comment: 15 pp + 11 Figures appended as Postscript file