The D*Dpi form factor is evaluated at low and moderate Q² in a hadronic loop model, for off-shell D mesons. The results contain arbitrary constants, which are fixed so as to match a previous QCD sum rule calculation valid at higher Q². The form factor obtained in this way is used to extract the coupling constant, which is in very good agreement with the experimental value.

The Interacting Gluon Model (IGM) is a tool designed to study energy flow, especially stopping and leading particle spectra, in high energy hadronic collisions. In this model, valence quarks fly through and the gluon clouds of the hadrons interact strongly both in the soft and in the semihard regime. Developing this picture we arrive at a simple description of energy loss, given in terms of few parameters, which accounts for a wide variety of experimental data. This text is a survey of our main results and predictions.

We calculate the J/psiD*D* form factor and coupling constant from QCD Sum Rules in the cases where J/psi and D* mesons are off-shell. The results show that this method is consistent and allows to extract the same coupling constant for the vertex.

In this work we calculate the meson cloud effects on the pion electromagnetic form factor and perform a comparison with experimental data. We show that, even though the cloud is not the only non-perturbative process to be considered, its contribution is significant. We also study the influence of the cutoff choices on the results.

We update the calculation of c - <img id="_x0000_i1026" src="../../img/revistas/bjp/v34n1a/a19img02.gif" align=absbottom>production in the initial stage of nucleus - nucleus collisions and within quark gluon plasma, using the most recent and most accepted values for the ingredients, such as nuclear parton distributions, quark masses, couplings and fireball parameters. We find a large discrepancy in the charm yields, depending on the input choices. A global analysis of all the different cases suggests that the “in-plasma” production is a significant fraction of the total yield.

In this work, we present calculations for the charmonium-hadron cross section. The hadron is represented by an external color field and the charmonium is represented by a small color dipole. Using high-energy approximations we compute the relevant cross sections, which agree with results obtained with other methods.

We employ QCD sum rules to calculate the J/psiDD* form factors and coupling constant by studying the threepoint J/psiD*D correlation function. We find that the momentum dependence of the form factor depends on the off-shell meson. We get a value for the coupling which is in agreement with estimates based on constituent quark model.

We study the Borel sum rule for the tensor amplitude of the processes J/<FONT FACE=Symbol>y p ®</FONT> <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*,<IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif"> D, <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >*D* and <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*. We also evaluate the cross sections as a function of <IMG SRC="/img/revistas/bjp/v33n2/a30img02.gif" >. We find that our results are smaller than the J/<FONT FACE=Symbol>y p ®</FONT> charmed mesons cross sections obtained with models based on meson exchange, but are close to those obtained with quark exchange models.

Recent DESY-HERA data on J/<FONT FACE="Symbol">Y</font> elasticity distribution show that it emerges mostly as a fast particle. Interpreting photoproduction as a collision between a pre-formed charmed hadron and the proton, the outcoming J/<FONT FACE="Symbol">Y</font> is a leading particle of the collision. We analyse these data using a model formulated to describe energy flow in hadron-hadron reactions. The measured J/<FONT FACE="Symbol">Y</font> spectrum can be successfully described in terms of this model. We conclude that the observed transparency of the charmed hadron-proton collisions arises because of the particularly small gluonic content of the initial c - <img src="http:/img/fbpe/bjp/v28n4/image200.gif" alt="Image200.gif (847 bytes)" align="absbottom"> state.

In this work we extend previous kaon loop calculations, including the vector K* meson and estimate the strangeness radius of the nucleon and its strange magnetic moment. We find out that, in contrast to naive expectations, this contribution is very important and gives large values for both the radius and the magnetic moment