2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/43425We have explicitly shown that the infrared structure of the full gluon propagator in QCD is an infite sum over all severe (i.e., more singular than $1/q^2$) infrared singularities. It reflects the zero momentum modes enhancement effect in the true QCD vacuum. Its existence exhibits a characteristic mass (the so-called mass gap), which is responsible for the scale of nonperturbative dynamics in the QCD ground state. By an infrared renormalization of a mass gap only, the deep infrared structure of the full gluon propagator is saturated by the simplest severe infrared singularity, the famous $(q^2)^{-2}$. So, there is no smooth in the infrared limit the full gluon propagator. The main dynamical source of severe infrared singularities in the gluon propagator is the two-loop skeleton term of the corresponding equation of motion, which contains the four-gluon vertices only. Taking into account the distribution nature of severe infrared singularities, the gluon confinement criterion is formulated in a manifestly gauge-invariant way.12 pages, no tables, no figures, multiplied typos are corrected, clarification is introducedHigh Energy Physics - Phenomenologytext