出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We show that the gauge invariant treatment of the Schwinger-Dyson equations of QCD leads to an
infrared finite gluon propagator, signaling the dynamical generation of an effective gluon mass,
and a non-enhanced ghost propagator, in qualitative agreement with recent lattice data. The truncation
scheme employed is based on the synergy between the pinch technique and the background
field method. One of its most powerful features is that the transversality of the gluon self-energy
is manifestly preserved, exactly as dictated by the BRST symmetry of the theory. We then explain,
for the first time in the literature, how to construct non-perturbatively a renormalization
group invariant quantity out of the conventional gluon propagator. This newly constructed quantity
serves as the natural starting point for defining a non-perturbative effective charge for QCD,
which constitutes, in all respects, the generalization in a non-Abelian context of the universal
QED effective charge. This strong effective charge displays asymptotic freedom in the ultraviolet,
while in the low-energy regime it freezes at a finite value, giving rise to an infrared fixed point
for QCD. Some possible pitfalls related to the extraction of such an effective charge from infrared
finite gluon propagators, such as those found on the lattice, are briefly discussed.
