[en] In the framework of QCD at finite temperature we have obtained dissipative terms for the effective potential between q and q-bar which would partly explain the J/ψ suppression in the Quark Gluon Plasma (QGP). The derivation of the dissipative potential for QGP is presented and the case for Hadron Matter (HM) is briefly discussed. The suppression effects are estimated based on simple approximations. (author). 16 refs., 1 fig

[en] We show that the confining term in the widely used Cornell form of QCD potential is derivable from the gluon superpropagator for an exponential form of gluon self-interaction, if one assumes that the gluon-gluon coupling constant has the character of a running coupling constant. We also consider a rational form of self-interaction. (author)

[en] A strategy for calculating the color structure needed for soft gluon resummation for processes with any number of colored partons is introduced using a N_c → ∞ inspired basis. In this basis a general formalism can be found at the same time as the calculations are simplified. The advantages are illustrated by recalculating the soft anomalous dimension matrix for the processes gg → gg, q q-bar → q q-bar g and q q-bar → ggg.

[en] Gluons are particles that generate the strong interaction among quarks and maintain the cohesiveness of the proton. Glueballs are systems made up of gluons and numerous physicists think that glueballs have been yet created in particle accelerators despite their short lifetime (10^-24 s), various detected elements whose mass ranges from 1500 to 1800 MeV are thought to be glueballs. In 1972 H. Fritzsch and M.Gell-Mann predicted the existence of glueballs as the only formation of gluons involving no quarks. (A.C.)

[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)

[en] We discuss what happens at the end of the QCD cascades. We show that, with just a few reasonable assumptions, the emission of soft gluons is constrained to produce an ordered field in the form of a helix. We describe how to modify the Lund fragmentation scheme in order to fragment such a field. Our modified fragmentation scheme yields results which are consistent with current experimental measurements, but predicts at least one signature which should be observable. (author)

[en] We report on the infrared limit of the quenched lattice Landau gauge gluon propagator computed from large asymmetric lattices. In particular, the compatibility of the pure power law infrared solution (q²)^2κ of the Dyson-Schwinger equations is investigated and the exponent k is measured. The lattice data favours κ ∼ 0.52, which would imply a vanishing zero momentum gluon propagator as predicted by the Kugo-Ojima confinement mechanism and the Zwanziger horizon condition. Results for the ghost propagator and for the running coupling constant are shown. (author)

[en] We consider QCD corrections to Higgs boson production through gluon--gluon fusion in hadron collisions. Using the recently evaluated two-loop amplitude for this process and the corresponding factorization formulae describing soft-gluon bremsstrahlung at O(α_S²), we compute the soft and virtual contributions to the next-to-next-to-leading order cross section. We also discuss soft-gluon resummation at next-to-next-to-leading logarithmic accuracy. Numerical results for Higgs boson production at the LHC are presented. (author)

[en] For about twenty years, the glueballs, hypothetical particles predicted by the quantum chromodynamics (QCD) theory, have never been detected with certainty. Thanks to extraordinary complex computer calculations, Donald Weingarten's team from the IBM research center of Yorktown Heights new New York (USA), have claimed that they are now able to define glueballs. According to their calculations, glueballs have been detected several times in the debris from the collision experiments carried out at the SLAC, the CERN or the Pekin Institute for High Energy Physics. A critical commentary of these affirmations is given by Pierre Fayet from the ENS (Ecole Normale Superieure of Paris, France). This short paper gives also a short recall of the gluon model and of glueballs properties according to QCD theory. (J.S.). 1 fig., 1 photo

[en] A typical signal of the formation of a plasma is the shielding of the mutual potential. A phenomenological shielding of a confining potential is here presented as a very simplified model of some possible features of a QCD (quantum chromodynamics) plasma. (author)