Calculating the decay constants in dynamical symmetry breaking

Physical quantities accompanying the dynamical chiral symmetry breaking in QCD like theories are examined. Expression for the decay constant (usually called fπ) is given exactly to the ladder approximation by solving the Bethe-Salpeter equation. Numerical calculation is done for Σ(self energy function of fermion), fπ, <ψ-barψ>R, with various β-function of the gauge coupling constant. We find that fπ/<ψ-barψ>R, fπ/ΛQCD are rather stable against the infrared cutoff parameter, while Σ-function itself depends strongly on the infrared cutoff. In this talk, I will describe very basic points of our framework and present some numerical results. (author)