A "natural" model for the QCD invariant (running) coupling, free of the IR singularity, is proposed. It is based upon the hypothesis of finite gluon mass $ m_{ gl}$ existence and, technically, uses an accurate treating of threshold behavior of Feynman diagram contribution. The model correlates with the unitarity condition. Quantitative estimate, performed in the one-loop approximation yields a reasonable lower bound for this mass $m_{ gl} > 150$ MeV and a smooth IR freezing at the level $\alpha_s(Q^2)\lesssim 1$.
Categories: hep-ph