  We discuss formulation of QCD in Minkowski-spacetime and effect of an
operator product expansion by means of normal ordering of fields in the QCD
Lagrangian. The formulation of QCD in the Minkowski-spacetime allows us to
solve a constraint equation and decompose the gauge field propagator in the sum
of an instantaneous part, which forms a bound state, and a retarded part, which
contains the relativistic corrections. In Quantum Field Theory, for a
Lagrangian with unordered operator fields, one can make normal ordering by
means of the operator product expansion, then the gluon condensate appear. This
gives us a natural way of obtaining a dimensional parameter in QCD, which is
missing in the QCD Lagrangian. We derive a Schwinger-Dyson equation for a
quark, which is studied both numerically and analytically. The critical value
of the strong coupling constant $\alpha_s = 4/{\pi}$, above which a nontrivial
solution appears and a spontaneous chiral symmetry breaking occurs, is found.
For the sake of simplicity, the considered model describes only one flavor
massless quark, but the methods can be used in more general case. The
Fourier-sine transform of a function with log-power asymptotic was performed.
