A. A. Natale

Phenomenological tests for the freezing of the QCD running coupling constant

We discuss phenomenological tests for the frozen infrared behavior of the running coupling constant and gluon propagators found in some solutions of Schwinger–Dyson equations of the gluonic sector of QCD. We verify that several observables can be used in order to select the different expressions of αs found in the literature. We test the effect of the nonperturbative coupling in the τ-lepton decay rate into nonstrange hadrons, in the ρ vector meson helicity density matrix that are produced in the χc2→ρρ decay, in the photon to pion transition form factor, and compute the cross-sections for elastic proton–proton scattering and exclusive ρ production in deep inelastic scattering. These quantities depend on the infrared behavior of the coupling constant at different levels, we discuss the reasons for this dependence and argue that the existent and future data can be used to test the approximations performed to solve the Schwinger–Dyson equations and they already seem to select one specific infrared behavior of the coupling.

Influence of a dynamical gluon mass in the pp and pp forward scattering

We compute the tree level cross section for gluon-gluon elastic scattering taking into account a dynamical gluon mass, and show that this mass scale is a natural regulator for this subprocess cross section. Using an eikonal approach in order to examine the relationship between this gluon-gluon scattering and the elastic pp and pp channels, we found that the dynamical gluon mass is of the same order of magnitude as the ad hoc infrared mass scale m{sub 0} underlying eikonalized QCD-inspired models. We argue that this correspondence is not an accidental result, and that this dynamical scale indeed represents the onset of nonperturbative contributions to the elastic hadron-hadron scattering. We apply the eikonal model with a dynamical infrared mass scale to obtain predictions for {sigma}{sub tot}{sup pp,pp}, {rho}{sup pp,pp}, slope B{sup pp,pp}, and differential elastic scattering cross section d{sigma}{sup pp}/dt at Tevatron and CERN-LHC energies.

NONLEPTONIC ANNIHILATION DECAYS OF B MESON WITH A NATURAL INFRARED CUTOFF

Within the QCD factorization approach we compute the amplitudes for pure annihilation channels of B mesons decays into final states containing two pseudoscalar particles. These decays may be plagued by effects like nonperturbative physics and breaking of the factorization hypothesis and imply, at some extent, the introduction of an infrared cutoff in the calculation of amplitudes. We compute the decays with the help of infrared finite gluon propagators and coupling constants that were obtained in different solutions of the QCD Schwinger–Dyson equations. These solutions yield a natural cutoff for the amplitudes, and we argue that a systematic study of these B decays may provide a test for the QCD infrared behavior.

The small x behavior of the gluon structure function from total cross-sections

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale we discuss how the small x behavior of the gluon distribution function at moderate Q2 is directly related to the rise of total hadronic cross-sections. In this model the rise of total cross-sections is driven by gluon–gluon semihard scattering processes, where the behavior of the small x gluon distribution function exhibits the power law xg(x, Q2) = h(Q2)x-∊. Assuming that the Q2 scale is proportional to the dynamical gluon mass one, we show that the values of h(Q2) obtained in this model are compatible with an earlier result based on a specific nonperturbative Pomeron model. We discuss the implications of this picture for the behavior of input valence-like gluon distributions at low resolution scales.

Phenomenology of infrared finite gluon propagator and coupling constant

We report on some recent solutions of the Dyson-Schwinger equations for the infrared behavior of the gluon propagator and coupling constant, discussing their differences and proposing that these different behaviors can be tested through hadronic phenomenology. We discuss which kind of phenomenological tests can be applied to the gluon propagator and coupling constant, how sensitive they are to the infrared region of momenta and what specific solution is preferred by the experimental data.

A Dynamical gluon mass solution in Mandelstam's approximation

We discuss the pure gauge Schwinger–Dyson equation for the gluon propagator in the Landau gauge within an approximation proposed by Mandelstam many years ago. We show that a dynamical gluon mass arises as a solution. This solution is obtained numerically in the full range of momenta that we have considered without the introduction of any ansatz or asymptotic expression in the infrared region. The vertex function that we use follows a prescription formulated by Cornwall to determine the existence of a dynamical gluon mass in the light cone gauge. The renormalization procedure differs from the one proposed by Mandelstam and allows for the possibility of a dynamical gluon mass. Some of the properties of this solution, such as its dependence on ΛQCD and its perturbative scaling behavior are also discussed.

DYNAMICAL SYMMETRY BREAKING IN A MINIMAL 3-3-1 MODEL

The gauge symmetry breaking in some versions of 3-3-1 models can be implemented dynamically because at the scale of a few TeVs the U(1)X coupling constant becomes strong. In this work, we consider the dynamical symmetry breaking in a minimal SU(3)TC × SU(3)L × U(1)X model, where we propose a new scheme to cancel the chiral anomalies, including two-index symmetric (6) technifermions, which incorporates naturally the walking behavior in the Technicolor (TC) sector. The composite scalar content of the model is minimal and all the symmetry breaking is implemented by a multiplet of technifermions. The choice of TC representations not only provides the anomaly cancelation with a walking behavior, but is crucial to promote the models full dynamical symmetry breaking. We consider the dynamical generation of technigluon masses and, depending on the 3-3-1 symmetry breaking scale (μ331), we verify that the technigluon mass is strongly linked to the Z′ mass scale, for instance, if μ331 = 1 TeV, we have MZ′ > 1 TeV only if MTG < 350 GeV.

A DYNAMICAL MECHANISM TO EXPLAIN THE TOP-BOTTOM QUARK MASS HIERARCHY

We discuss the mass splitting between the the top and bottom quarks in a technicolor scenario. The model proposed here contains a left–right electroweak gauge group. An extended technicolor group and mirror fermions are introduced. The top-bottom quark mass splitting turns out to be intimately connected to the breaking of the left–right gauge symmetry. Weak isospin violation occurs within the experimental limits.

Preliminary Results on the Influence of a Gluon Mass in Hadronic Scattering

We present a description of the experimental data on forward pp and pp elastic scattering by means of a QCD‐inspired model implemented with a dynamical gluon mass.

Chiral symmetry breaking with a confining propagator and dynamically massive gluons

Chiral symmetry breaking in QCD is studied introducing a confining effective propagator, as proposed recently by Cornwall, and considering the effect of dynamically massive gluons. The effective confining propagator has the form