Repositório RCAAP

After reviewing the main aspects of the model-independent analysis on elastic proton-proton scattering, developed by França and Hama in the seventies, we argue that the work can be considered a paradigm for empirical analysis on elastic hadron interactions (the inverse problem). We discuss some further developments, consequences and results that have been recently obtained on the subject and which have been based on the original strategy by França and Hama.

We make a brief review of the Kramers escape rate theory for the probabilistic motion of a particle in a potential well U(x), and under the influence of classical fluctuation forces. The Kramers theory is extended in order to take into account the action of the thermal and zero-point random electromagnetic fields on a charged particle. The result is physically relevant because we get a non null escape rate over the potential barrier at low temperatures (T -> 0). It is found that, even if the mean energy is much smaller than the barrier height, the classical particle can escape from the potential well due to the action of the zero-point fluctuating fields. These stochastic effects can be used to give a classical interpretation to some quantum tunneling phenomena. Relevant experimental data are used to illustrate the theoretical results.

The hadronic structure is investigated in terms of a recently proposed theory which considers the effect of the strong interaction in the space-time description. From the equations, the masses of the particles may be calculated, and quark confinement appears as a natural result, without the need of confining potentials. Some properties of the considered particles, such as the topponium size, are also estimated.

We discuss macroscopic aspects of quark matter phase transition in cold dense stellar matter, considering global charge neutrality and baryonic charge conservation. We determine the critical condition for the phase transition between the strange quark matter, SQM, and the color-flavor locked, CFL, superconducting phase. We also discuss the sensitivity of our results to variations in the gap energy, delta, and in the current strange quark mass, m s0. The phase transition is calculated taking into account the baryonic density dependence of the quark masses in dense baryonic medium.

We present a construction of an effective Yang-Mills action for QCD, from the expansion of the fermionic determinant in terms of powers of the chemical potential at high temperature for the case of massless quarks. We analyze this expansion in the perturbative region and find that it gives extra spurious information. We propose for the non-perturbative sector a simplified effective action which, in principle, contains only the relevant information.

Recent results for the two-loop thermodynamic potential of QCD at finite density have shown that nonzero quark mass corrections to the pressure are relevant and can dramatically affect the structure of compact stars. Motivated by these findings, we consider a simple toy model - cold and dense Yukawa theory - to study the effects of finite fermion masses on the pressure. The role of renormalization group running of the coupling and mass is also discussed. Results within this simple model might be useful in the description of condensates in the core of neutron stars.

In this paper we discuss the semiclassical approximation for the thermodynamics of scalar fields. We construct a semiclassical propagator in terms of two solutions of an ordinary differential equation. The main result is an analytic (non-perturbative) expression for the partition function written in terms of known quantities.

The linear sigma model at finite baryonic density with a massive vector field is investigated considering that all the bosonic fields develop non zero expected classical values, eventually associated with condensates and corresponding to dynamical symmetry breakings which might occur in the QCD phase diagram. A modified equation for the classical vector field is proposed with its respective solution. Some in medium properties of the model (mainly masses) are investigated within reasonable prescriptions. In particular the behavior of the in medium pion and sigma masses and a particular way of calculating in medium coupling to baryons is investigated. A symmetry radius for finite baryonic densities is proposed and calculated in different ways in terms of the other variables of the model and these different ways of calculating it agree quite well. However, assuming that the pion and sigma masses go to zero close to the restoration of chiral symmetry a too high value for the critical density is obtained rhoc <FONT FACE=Symbol>@</FONT> 4.3 rho0.

This work is concerned with non-equilibrium phenomena, with focus on the numerical simulation of the relaxation of non-conserved order parameters described by stochastic kinetic equations known as Ginzburg-Landau-Langevin (GLL) equations. We propose methods for solving numerically these type of equations, with additive and multiplicative noises. Illustrative applications of the methods are presented for different GLL equations, with emphasis on equations incorporating memory effects.

In this work we present a study of the influence of nucleus initializations on the event-by-event elliptic flow coefficient, v2. In most Monte-Carlo models, the initial positions of the nucleons in a nucleus are completely uncorrelated, which can lead to very high density regions. In a simple, yet more realistic model where overlapping of the nucleons is avoided, fluctuations in the initial conditions are reduced. However, v2 distributions are not very sensitive to the initialization choice.

An inhomogeneous decoupling surface of hadrons produced in relativistic heavy-ion collisions may occur, if the expanding hot and dense matter passes through a first order phase transition. We show that due to the non-linear dependence of the particle densities on the temperature and baryon-chemical potential such inhomogeneities should be visible even in the integrated, inclusive abundances. We analyze experimental data from Pb+Pb collisions at CERN-SPS and Au+Au collisions at BNL-RHIC to determine the amplitude of inhomogeneities and the role of local and global strangeness neutrality.

We analyze the cosmic ray arrival direction map that would be observed if the source of ultra high energy cosmic rays were the decay of dark matter particles in the halos of our galaxy and of the Andromeda galaxy (M31). To model the dark matter distribution throughout the halos we use two different density profiles, the Moore et al. and the Navarro-Frenk-White profile. The results show what would be seen by the Pierre Auger experiment, since we take into account its exposure. We evaluate the dipole and quadrupole terms for the resulting maps in the two density profiles cases and compare them with the terms expected for an isotropic sky.

The recent discovery of a new and intense solar flare radiation spectral component with a maximum in the terahertz range has raised a great deal of interest. The origin of this component is still unknown, constituting a problem that goes beyond the application of canonical models used to describe the well-known microwave spectrum. In this work, we present preliminary results on the investigation of a possible contribution from electron-positron pairs produced in a Drell-Yan process to the emission of the terahertz component observed in solar flares.

Using the QCD sum rule approach we investigate the vertex associated with the decay D0(0+)-> D+pi-, where the scalar meson D0(0+) is considered as a four-quark state $(cd)(\bar{u}\bar{d})$. Although our results for the mass and partial decay width are smaller than the mass and the total decay width of the broad scalar meson D0*0(2308) reported by BELLE Collaboration, we can not discard the possibility that the BELLE's resonance can be interpreted as the four-quark state studied here.

We calculate the coupling constants of D*Ds K and Ds*DK vertices using the QCD sum rules technique. We compare our results with results obtained in the limit of SU(4) symmetry and we found that the symmetry is broken at the order of 40%.

QCD spectral sum rules is used to test the nature of the meson X(3872), assumed to be an exotic four-quark $(c\bar{c}q\bar{q})$ state with J PC = 1++. For definiteness, the current proposed recently by Maiani et al [1] is used, at leading order in alphas, considering the contributions of higher dimension condensates. The value M X = (3.94±0.11) GeV is found which is compatible, within the errors, with the experimental candidate X(3872). The uncertainties of our estimates are mainly due to the one from the c quark mass.

In this work, we evaluate the D+sJ(2317), D(0)0(2308), D(0)0(2407) and D+0(2403) masses. These are scalar mesons recently discovered in the BABAR, BELLE and FOCUS Collaborations. The nature of these particles is intensely discussed nowadays. We treat them as a diquark-antidiquark configuration and treat the problem using the QCD sum rules (QCDSR) approach.

From the mass term for q-deformed quark fields, we obtain effective contact interactions of the NJL type. The parameters of the model that maps a system of non-interacting deformed fields into quarks interacting via NJL contact terms is discussed.

In our recent works we derived a chiral O(q4) two-pion exchange nucleon-nucleon potential (TPEP) formulated in a relativistic baryon (RB) framework, expressed in terms of the so called low energy constants (LECs) and functions representing covariant loop integrations. In order to facilitate the use of the potential in nuclear applications, we present a parametrized version of our configuration space TPEP.

Making use of a model-independent analytical fit for the elastic hadron-hadron amplitude, recently developed, we investigate the slope of the proton-proton and antiproton-proton differential cross sections, as a function of the energy and the momentum transfer. We show that the predictions for these quantities are in agreement with the experimental data available and discuss the effect of the slope position as function of the momentum transfer.