The Walecka many-body field theory is investigated in the context of quantum nonextensive statistical mechanics, characterized by a dimensionless parameter q. In this paper, we consider nuclear matter described statistically by a power-law distribution which generalizes the standard Fermi-Dirac distribution (q = 1). We show that the scalar and vector meson fields become more intense due to the nonextensive effects (q = 1). From a numerical treatment, we also show that as the nonextensive parameter q increases, the nucleon effective mass diminishes and the equation of state becomes stiffer. Finally, the usual Maxwell construction seems not to be necessary for isotherms with temperatures in the range 14Mev < kBT < 20MeV.

The eikonal profile function J(b) obtained from the Model of the Stochastic Vacuum is parametrized in a form suitable for comparison with experiment. The amplitude and the extended profile function (including imaginary and real parts) are determined directly from the complete pp andpp elastic scattering data at high energies. Full and accurate representation of the data is presented, with smooth energy dependence of all parameters. The changes needed in the original profile function required for description of scattering beyond the forward direction are described.

By using a q-calculus, the Walecka many-body field theory was studied in the context of the Tsallis framework. The most important aspect of the application of the q-calculus to the nonadditive formulation of QHD-I is that it naturally emerges as a thermodynamically consistent theory.

We investigate nonextensive effects on phase transition in nuclear matter in the context Walecka many-body field theory. Changes in the general behaviour are observed when the results calculated for the nuclear matter at vanishing baryon density are compared to those obtained through the standard Fermi-Dirac distribution. It is observed a dependence between the nonextensive parameter q and the coupling constants C 2 S of the phase transition. A numerical relation for this thermodynamical dependence is also proposed.PACS numbers: 21.65.+f; 26.60.+c; 25.75.-q

The dips observed in the differential cross sections of elastic pp and pp scattering are studied in terms of the locations of the zeros of the real and imaginary parts of the amplitude and of the sign of real part at large |t|. It is confirmed that the differences in shapes of the dips in the pp and pp systems are determined by a change of sign of the real tail, which seems to be determined by perturbative QCD contributions.

The two independent correlation functions describing nonperturbative properties of the QCD vacuum are taken into account in the evaluation of the observables of soft high-energy hadron-hadron scattering. The model of the stochastic vacuum provides the framework in which a simple and effective description of the high-energy pp and pp data can be given, leading to a determination of relevant parameters of nonperturbative QCD and to a good description of the data. The ratio between the non-Abelian and the Abelian parts of the field correlations is studied in terms only of high-energy data and the results are compared to lattice calculations. It is shown that a slow increase of the hadronic radii with the energy accounts for the energy dependence of all observables.

The functional dependence of the high-energy observables of total cross section and slope parameter on the sizes of the colliding hadrons predicted by the model of the stochastic vacuum and the corresponding relations used in the geometric model of Povh and H\"ufner are confronted with the experimental data. The existence of a universal term in the expression for the slope, due purely to vacuum effects, independent of the energy and of the particular hadronic system, is investigated. Accounting for the two independent correlation functions of the QCD vacuum, we improve the simple and consistent description given by the model of the stochastic vacuum to the high-energy pp and pbar-p data, with a new determination of parameters of non-perturbative QCD. The increase of the hadronic radii with the energy accounts for the energy dependence of the observables.Comment: Latex, using Revtex.style . 2 ps figures. To be published in Physical Review D , July 199

By using the recent nonperturbative equation of state of the quark gluon plasma derived in the formalism of the Field Correlator Method, we investigate the bulk properties of the strange quark matter in beta-equilibrium and with charge neutrality at T=p=0. The results show that the stability of strange quark matter with respect to $^{56}Fe$ is strongly dependent on the model parameters, namely, the gluon condensate $G_2$ and the q$\bar{\rm q}$ interaction potential $V_1$. A remarkable result is that the width of the stability window decreases as $V_1$ increases, being maximum at $V_1=0$ and nearly zero at $V_1=0.5$ GeV. For $V_1$ in the range $0\leq V_1\leq0.5$ GeV, all values of $G_2$ are lower than $0.006-0.007\;{\rm GeV}^4$ obtained from comparison with lattice results at $T_c\;(\mu=0)\sim170$ MeV. These results do not favor the possibilities for the existence of (either nonnegative or negative) absolutely stable strange quark matter