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[en] Full text: The present work concerns the ghost-gluon vertex of quantum chromodynamics, which, according to the Taylor identity, has no perturbative corrections to any order, in the Landau gauge and for a specific momentum configuration. We study this vertex for a momentum configuration for which there is no proof of such a result, which is the one with a zero gluon momentum. The framework we adopt for it is the 'Dynamical Perturbation Theory' approach, which consists of inserting some nonperturbative character of the theory into its perturbative expansion. It is a phenomenological attempt only, intended to probe infrared properties of the theory by means of loop calculations. We have made use of two nonperturbative properties: first, a finite gluon mass, since there are even more indications that the gluon presents a mass, though it is a dynamical one - it intrinsically changes from finite in the infrared, to zero in the ultraviolet. Second, a recent result on the effective charge of quantum chromodynamics, which itself considers a dynamical gluon mass. We calculate the 1-loop correction to the ghost-gluon vertex, aiming at verifying how close to 1 the ghost-gluon vertex renormalization function is. The result obtained was positive in this direction: indeed, it does not differ much from unity. Moreover, our result fits better the lattice data when we consider the mentioned effective charge, than when we set the coupling constant as a fit parameter. Therefore, our somewhat phenomenological approach based on a dynamical gluon mass is, at least, consistent, and supports the approximation, usually performed in the study of the Schwinger-Dyson equations of quantum chromodynamics, of the ghost-gluon vertex renormalization function to be identically equal to 1. (author)

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[en] Short communication

[en] Full text: In the phenomenology of strong interactions one always has to deal at some extent with the interplay between perturbative and non-perturbative QCD. On one hand, the former has quite developed tools, yielded by asymptotic freedom. On the other, concerning the latter, we nowadays envisage the following scenario: 1) There are strong evidences for a dynamically massive gluon propagator and infrared finite coupling constant; 2) There is an extensive and successful use of an infrared finite coupling constant in phenomenological calculations at tree level; 3) The infrared finite coupling improves the perturbative series convergence; 4) The dynamical gluon mass provides a natural infrared cutoff in the physical processes at the tree level. Considering this scenario it is natural to ask how these non-perturbative results can be used in perturbative calculations of physical observables at the loop level. Recent papers discuss how off-shell gauge and renormalization group invariant Green functions can be computed with the use of the Pinch Technique (PT), with IR divergences removed by the dynamical gluon mass, and using a well defined effective charge. In this work we improve the former results by the authors, which evaluate 1-loop corrections to some two- and three-point functions of SU(3) pure Yang-Mills, investigating the dressing of quantities that could account for an extension of loop calculations to the infrared domain of the theory, in a way applicable to phenomenological calculations. One of these improvements is maintaining the gluon propagator transverse in such a scheme. (author)

No abstract available