Repositório RCAAP

We discuss some phenomenological applications of an infrared finite gluon propagator characterized by a dynamically generated gluon mass. In particular we compute the effect of the dynamical gluon mass on pp and ${\bar{p}}p$ diffractive scattering. We also show how the data on gammap photoproduction and hadronic <FONT FACE=Symbol>gg</FONT> reactions can be derived from the pp and ${\bar{p}}p$ forward scattering amplitudes by assuming vector meson dominance and the additive quark model.

We evaluate nucleon and delta sigma-terms and obtain the results 43 MeV < sigmaN < 49 MeV and 28 MeV < <FONT FACE=Symbol>sD</FONT> < 32 MeV, depending on the coupling constants used, which are compatible with values extracted from experiment and produced by other groups. We show that the decay <FONT FACE=Symbol>D ® p</FONT>N explains the relation <FONT FACE=Symbol>sD</FONT> < sigmaN.

We study the conditions for the formation and propagation of Korteweg-de Vries solitons in relativistic fluid dynamics using an appropriate equation of state. The KdV equation is obtained from the relativistic version of the Euler and continuity equations.

Some consequences of the presence of critical point in the equation of state on the hydrodynamical evolution of the strongly interacting matter are discussed. For this purpose, we apply the low energy effective theory of QCD, the Nambu-Jona-Lasinio model and show some examples.

Elliptic flow at RHIC is computed event by event with NeXSPheRIO. Reasonable agreement with experimental data on v2(eta) and v2(pt) is obtained. Various effects are studied as well: equation of state (with or without critical point), emission mechanism (Cooper-Frye prescription or continuous emission), type of the initial conditions (average or fluctuating initial conditions).

We present a new formalism for the relativistic dissipative hydrodynamics consistent with causality. We start from the physical analysis of the irreversible currents according to the Landau-Lifshitz theory. Then, the irreversible currents are given by integral expressions which take into account the relaxation time. Only one additional parameter was introduced, the relaxation time, tauR. We verified that the linearized equation of motion for small perturbations in the homogeneous, static background coincides with Hiscock-Lindblom.

We report on our recent investigations in photonuclear production of heavy quarks and vector mesons in ultraperipheral collisions at nucleus-nucleus and proton-nucleus reactions. They are initiated by quasi-real photons coming from one of the nuclei or hadron in interactions taking place at large impact parameter. We focus on the role played by the high energy theoretical/phenomenological approaches in photon-nuclei scattering, namely the strength of parton saturation phenomenon and high energy nuclear shadowing. In particular, our theoretical predictions are compared with the recent experimental measurements on coherent r (STAR) and J/Y (PHENIX) photoproduction at RHIC and estimates for LHC are given.

We study proton - anti-proton cross sections in the framework of an updated minijet eikonal model. We propose a different scheme for fixing the parameters, in which we make use of the measured minijet cross section. We compare the results obtained with the GRV98, MRST98, CTEQ6-L and KLN gluon distributions. The latter includes gluon saturation effects. We conclude that in the very high energy regime the use of the KLN distribution improves significantly the behavior of the cross sections. However this improvement is due to the shape of the KLN gluon density and has little to do with saturation effects.

In this work we calculate the J/psi production in the initial stage of proton-proton, proton-nucleus and nucleus-nucleus collisions at RHIC and LHC energies, taking into account the high parton density regime of QCD, where the physics of parton saturation is expected to be dominant. We perform a quantitative analysis of the xF distributions in these collisions with the Color Glass Condensate (CGC) approach. The ratio between distributions with or without saturated gluons shows that this mechanism produces a suppression on the J/psi yield in the forward region and presents a dip in intermediate values of xF, which is visible only at LHC energies.

We study the predictions of CGC physics for electron-ion collisions at high energies. The nucleus at high energies acts as an amplifier of saturation effects. We have investigated some observables, using a generalization for nuclear targets of the Iancu-Itakura-Munier model, and our results indicate that the experimental analysis of these observables in the future electron-ion collider could discriminate between linear and saturation physics, as well as constrain the behavior of the saturation scale.

In this work we use the IGM, a model that describes well the energy flux in hadronic collisions, to study the leading particle spectrum when saturation effects on the gluon distribution function are included. The leading particle spectrum is calculated for several center of mass energies (<FONT FACE=Symbol>Ö</FONT>s). In the very high energy limit we compare our results with the predictions made in a recent paper, which also addresses the same problem.

No summary/description provided

We consider a local, renormalizable, BRST-invariant action for QCD in Coulomb gauge that contains auxiliary bose and fermi ghost fields. It possess a non-perturbative vacuum that spontaneously breaks BRST-invariance. The vacuum condition leads to a gap equation that introduces a mass scale. Calculations are done to one-loop order in a perturbative expansion about this vacuum. They are free of the finite-T infrared divergences found by Lindé and which occur in the order g6 corrections to the Stefan-Boltzmann equation of state. We obtain a finite result for these corrections. Renormalization and renormalization-group flow are described. We calculate the ghost propagator and color-Coulomb potential to one-loop and find that they are long range, whereas the 3-dimensionally transverse would-be physical gluon propagator is suppressed like k² at small |k|. These one-loop results accord with the Gribov scenario in Coulomb gauge and with recent numerical determinations of these quantities. When the auxiliary fields are integrated out, one obtains the standard Coulomb gauge action with a cut-off at the Gribov horizon.

In a functional approach to QCD the infrared behaviour of Landau gauge Green functions is investigated. It can be proven that the ghost Dyson-Schwinger equation implies the Gribov-Zwanziger horizon condition. Its relation to the Kugo-Ojima confinement scenario is elucidated. Positivity violation for gluons is demonstrated, and the analytic structure of the gluon propagator is studied. Quark confinement is related to an infrared divergence of the quark-gluon vertex. It is shown that in the latter various components are non-vanishing due to the dynamical breaking of chiral symmetry. As a result an infrared finite running coupling in the Yang-Mills sector is derived whereas the running coupling related to the quark-gluon vertex is infrared divergent. In Coulomb gauge QCD already the one-gluon-exchange (over-)confines. This leads to a vanishing quark propagator, and thus quarks are confined. Nevertheless colour singlet quantities derived from the quark propagator are well-defined. Especially the expression for the quark condensate proves that chiral symmetry is dynamically broken. As expected the properties of mesons can be directly calculated whereas the mass of coloured diquarks diverges, and thus diquarks are confined. The latter nevertheless possess a well-defined size. In the third part the results obtained so far will be used to formulate a covariant Faddeev approach to nucleons. The resulting amplitudes describe the quark core of the nucleon. Besides the mass of this state also the electromagnetic form factors are calculated. The results for charge radii and magnetic moments as a function of the quark current mass provide some indication what the missing pion cloud may contribute to the nucleons' properties.

We discuss the relation between lattice phenomenology of confining fields in the vacuum state of Yang-Mills theories (mostly SU(2) case) and continuum theories. In the continuum, understanding of the confinement is most straightforward in the dual formulation which involves higher dimensions. We try to bridge these two approaches to the confinement, let it be on a rudimentary level. We review lattice data on low-dimensional vacuum defects, like monopoles, center vortices. There is certain resemblance to dual strings, domain walls considered in the continuum version of Yang-Mills theories.

Effects of the quark field on the ghost propagator of the lattice Landau gauge are investigated by using the unquenched SU(3) configurations produced by the MILC collaboration and compared with quenched gauge configurations of SU(2) first copy of the overrelaxation gauge fixing, the parallel tempering (PT) gauge fixing and quenched SU(3) 56(4) configurations. We measure the color symmetric and the color antisymmetric ghost propagator and the Binder cumulant of the l¹ norm and the l² norm of color antisymmetric ghost propagators and investigate deviation from those of Gaussian distributions. In the first copy samples of quenched SU(2) we observe a large fluctuation in the Binder cumulant at the lowest momentum point. This fluctuation is reduced in the PT gauge fixed samples. The color anti-symmetric ghost propagator of quenched SU(3) configurations depends on the lattice size and is small as compared to the symmetric one in the large lattice of 56(4). The Binder cumulants of the quenched SU(2) and the Nf = 2 + 1 unquenched SU(3) are almost consistent with 3-d and 8-d Gaussian distribution, respectively. A comparison of the SU(3) unquenched configurations and quenched configurations indicates that the dynamical quarks have the effect of making color antisymmetric ghost propagator closer to the Gaussian distribution and the Kugo-Ojima color confinement parameter c closer to 1.

We report on recent numerical computations of the Landau gauge gluon and ghost propagators as well as of the ghost-gluon-vertex function in pure SU(3) Yang-Mills theory and in full QCD on the lattice. Special emphasis is paid to the low momentum region. In particular, we present new data for the gluon propagator at momenta below 300 MeV. We also discuss different systematic effects as there are finite-size, lattice discretization and Gribov copy but also unquenching effects. A MOM-scheme running coupling alphas(q²) based on the ghost-gluon vertex is calculated and found to decrease for momenta below 550 MeV, even though the renormalization constant of the vertex deviates only weakly from being constant.

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)²kappa of the Dyson-Schwinger equations is investigated and the exponent kappa is measured. The lattice data favours kappa ~ 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.

The order and the universality class of the deconfining phase transition can provide insight into the mechanism of color confinement, in particular for Nf = 2. The mechanism of confinement by monopole condensation is reviewed.

The configuration space of SU(N) gauge theory is restricted to orbits with vanishing Polyakov loops of non-trivial N-ality. A practical method of constraining to this orbit space C0 is found by implementing a certain axial-type gauge. It is shown that the representative of an orbit in C0 is unique in this gauge up to time independent Abelian gauge transformations. The restricted orbit space does not admit non-Abelian monopoles. As long as C0 is thermodynamically stable, the free energy of the constrained SU(N) gauge model is of order N0 (even in the presence of dynamical quarks) and confinement is manifest for sufficiently large N. With a free energy of order N0 and Polyakov loops that vanish by design, there is no transition that deconfines color charge in such an SU(N) model. However, a proliferation of massless hadronic states of arbitrary spin could lead to a Hagedorn transition[1] if the string tension vanishes at a finite temperature T H. Constraining the orbit space to C0 can be viewed as a particular boundary condition, and T H in general is above the first order deconfinement transition of the full theory at Td. Between Td and T H a superheated confining phase may exist for SU(N > 2). Perturbation theory in C0 is sketched. It does not suffer from the severe IR-divergences observed by Linde[2]for the ordinary high temperature expansion. Correlations of the lowest transverse Abelian Matsubara modes develop a renormalization group invariant pole of second order at vanishing spatial momentum transfer when T = T H. The latter could be associated with linear confinement.