Vacuum Instability and New Constraints on Fermion Masses

I show that, in the Weinberg-Salam model with one Higgs doublet, in order for the physical vacuum to be an absolute minimum (in the one-loop approximation), certain requirements on the fermion masses have to be met. Specifically, the quantity Σi^m_fᵢ⁴1/4, where the summation extends over fermions, is bounded from above by approximately 133.5 GeV (sin²θW=0.25) or 137.7 GeV (sin²θW=0.2).