Resumo em Inglês:

According to a variety of cosmological observations at small and large redshifts, the universe is composed by a large fraction of a weakly clustered component with negative pressure, called dark energy. The nature of the dark energy, i.e. its interaction and self-interaction properties, is still largely unknown. In this contribution we review the properties of dark energy as inferred from observations, with particular emphasis on the cosmic microwave background. We argue that the current dataset imposes strong constraints on the coupling of dark energy to dark matter, while it is still insufficient to constrain the equation of state or potential. Future data will dramatically improve the prospects.

Resumo em Inglês:

Noncommutative field theories present many surprising properties. As a consequence of the noncommutativity, high momentum modes do not decouple from the physics at large distances leading to the appearance of infrared singularities even in theories without massless particles. Being nonintegrable, these infrared singularities destroy the usual perturbative expansions. We discuss talk alternative procedures to, we examine control this situation. In the low momentum regime of the Wess-Zumino model the e ect of the underlying nonlocality on the nonrelativistic potential will be examined and some physical implications.

Resumo em Inglês:

We discuss the production of hadronic resonances in very peripheral heavy ion collisions, where the ions collide with impact parameter larger than twice the nuclear radius and remain intact after the collision. We compare the resonance production through two-photon and double Pomeron exchange, showing that when we impose the condition for a peripheral interaction the <FONT FACE=Symbol>gg</FONT> process dominates over the Pomeron interaction, due to the short range propagation of this last one. We also discuss the observation of light resonances through the subprocess <FONT FACE=Symbol>gg</FONT> ->R <FONT FACE=Symbol>®gg</FONT> , which is a clean signal for glueball candidates as well as one way to check the existence of a possible scalar sigma meson.

Resumo em Inglês:

It is known that the associativity of the star product of the open string field theory may be broken in the presence of the nontrivial closed string background. We give an argument that such an anomaly may be resolved by including Chan-Paton factors starting from the axioms of the rational conformal field theory.

Resumo em Inglês:

The first phase of the Brazilian Graviton Project is the construction and operation of the gravitational wave detector Mario Schenberg at the Physics Institute of the University of São Paulo. This gravitational wave spherical antenna is planned to feature a sensitivity better than h = 10-21 Hz-1/2 at the 3.0-3.4 kHz bandwidth, and to work not only as a detector, but also as a testbed for the development of new technologies. Here we present the status of this detector.

Resumo em Inglês:

In this work we review some features of topological defects in field theory models for real scalar fields. We investigate topological defects in models involving one and two or more real scalar fields. In models involving a single field we examine two different subclasses of models, which support one or more topological defects. In models involving two or more real scalar fields, we explore the presence of defects that live inside topological defects, and junctions and networks of defects. In the case of junctions of defects we investigte structures that simulate nanotubes and fulerenes. Our investigations may also be used to describe nonlinear properties of polymers, Langmuir films and optical solitons in fibers.

Resumo em Inglês:

We review the relation between the Maldacena conjecture, also known as AdS=CFT correspondence, and the so-called holographic principle that seems to be an essential ingredient for a quantum gravity theory. We also illustrate the idea of holography by showing that the curvature of the anti-de Sitter space reduces the number of degrees of freedom making it possible to find a mapping between a quantum theory defined on the bulk and another defined on the corresponding boundary.

Resumo em Inglês:

This is a short review of the derivation of the spectrum of the Dirac operator in QCD4 in a finite volume V by means of the replica trick. The derivation is nonperturbative in the QCD coupling and it is in agreement with lattice results as well as chiral random matrix theory (ChRMT). Our results hold in the energy scale where chiral symmetry is broken and the Pion wavelength is much bigger than the size of the system (<IMG SRC="/img/fbpe/bjp/v32n4/a11img02.gif">pi >>> V ¼).

Resumo em Inglês:

We review the work done by our group on cosmic topology. It ranges from early atempts to solve a famous controversy about quasars thought the multiplicity of images, to quantum cosmology in this context and an application to QED renormalization.

Resumo em Inglês:

We discuss the status of the Pierre Auger Observatory. The construction of the southern site in Argentina has started a year and a half ago. The project is in its first phase which consists in the construction and running of the so-called engineering array, a prototype of the experiment. The goals, design and construction of the observatory are discussed.

Resumo em Inglês:

We present a summary of the contribuitions on Field Theory at the XXII Brazilian National Meeting on Particles and fields.

Resumo em Inglês:

The plenary lectures, parallel talks, oral presentations and poster contribuitions on Cosmology and Gravitation presented during the XXII Brazilian National Meeting on Particles and fields are briefly reviewed. Some general remarks are also presented.

Resumo em Inglês:

The mechanism for ion neutralization at metal surfaces via surface plasmon excitation was previously suggested. It was shown that this mechanism is of comparable probability as the other two well studied mechanisms, namely, Auger and resonance tunneling neutralizations. In the present work we study the probability of exciting a bulk rather than surface plasmon during the neutralization process. The calculations show that the neutralization rate depends exponentially on the ion distance from the surface. And it is found to be important at small distances from the surface. The theory is applied to the scattering of protons from aluminium surface. Comparison between the transition rate for bulk plamon-assisted and surface plasmon-assisted and surface plasmon-assisted ion neutralization shows that the transition rate is lower by two orders of magnitude in the case of bulk plasmon-assisted neutralization as was expected.

Resumo em Inglês:

We discuss how resonance micro-Raman spectroscopy can determine the electronic and structural properties of individual isolated single-wall carbon nanotubes (SWNTs) that can be further used for potential nanodevices or studied by different experimental techniques. We show that it is possible to mark the surface of the Si/SiO2 substrate for localization of the isolated SWNTs by using a diamond tip. By timing the growth procedure, a low density of SWNTs on the substrate can be obtained so that the SWNT localization by atomic force microscopy (AFM) is trivial. We also characterize a SWNT by resonance Raman spectroscopy at the edge of a Si-SWNT-AFM tip. There results show that it is possible to make joint experiments on the same isolated SWNT.

Resumo em Inglês:

The physics of active galactic nuclei (AGN) and related objects is one of the most actively pursued areas of astrophysics. Their large luminosities over the entire electromagnetic spectrum combined with extremely short time variability has stimulated a large number of astrophysicists to propose rather unconventional ideas. A variety of radiation mechanisms such as, thermal, synchrotron and Compton processes have been proposed to account for the complex continuum emission. It is only recently that the role of plasma radiation mechanisms has been shown to be of the utmost impor tance. It is demonstrated how a combination of the stimulated Raman and Compton scattering processes accounts for the major part of the spectrum, taking 3C273 as an example. In addition plasma mechanisms for, the heating of the emission line regions, absorption of 21 cm radiation, producing time variability on different time scales and pair production and annihilation are also discussed.

Resumo em Inglês:

We study the thermodynamic properties of a semiexible polymer confined inside strips of widths L <= 9 defined on a square lattice. The polymer is modeled as a self-avoiding walk and a short-range interaction between the monomers and the walls is included through an energy <IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif">associated with each monomer placed on one of the walls. Also, an energy <IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif">b is associated with each elementary bend of the walk. The free energy of the model is obtained exactly through a transfer matrix formalism. The profile of monomer density and the force on the walls are obtained. We notice that as <IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif">b is decreased, the range of values of <IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif">which the density profi le is neither convex nor concave increases, and for sufficiently attracting walls (<IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif"> < 0) we find that in general the attractive force is maximum for <IMG SRC="/img/fbpe/bjp/v32n4/a19img04.gif">b < 0, that is, for situations where the bends are favored.

Resumo em Inglês:

A Green's function theory is applied to the description of luminescence and absorption spectra of low dimensional semiconductors. Progress in the numerical solution of the Bethe Salpeter equation for coupled band quantum wells with a T-matrix structure for the polarisation function and carrier-carrier dephasing is given within an approach that satisfy the Kubo-Martin-Schwinger sum rule and eliminates typical artifacts in computed optical spectra.

Resumo em Inglês:

The compressible magnetohydrodynamic Kelvin-Helmholtz instability occurs in two varieties, one that can be called incompressible as it exists in the limit of vanishing compressibility (primary instability), while the other exists only when compressibility is included in the model (secondary instability). In previous work we developed techniques to investigate the stability of a surface of discontinuity between two different uniform ows. Our treatment includes arbitrary jumps of the velocity and magnetic fields as well as of density and temperature, with no restriction on the wave vector of the modes. Then it allows stability analyses of complex configurations not previously studied in detail. Here we apply our methods to investigate the stability of various typical situations occurring at different regions of the front side, and the near anks of the magnetopause. The physical conditions of the vector and scalar fields that characterize the equilibrium interface at the positions considered are obtained both from experimental data and from results of simulation codes of the magnetosheath available in the literature. We give particular attention to the compressible modes in configurations in which the incompressible modes are stabilized by the magnetic shear. For configurations of the front of the magnetopause, which have small relative velocities, we find that the incompressible MHD model gives reliable estimates of their stability, and compressibility effects do not introduce significant changes. However, at the anks of the magnetopause the occurrence of the secondary instability and the shift of the boundary of the primary instability play an important role. Consequently, configurations that are stable if compressibility is neglected turn out to be unstable when it is considered and the stability properties are quite sensitive on the values of the parameters. Then compressibility should be taken into account when assessing the stability properties of these configurations, since the estimates based on incompressible MHD may be misleading. A careful analysis is required in each case, since no simple rule of thumb can be given.

Resumo em Inglês:

This paper is a survey on Symplectic Integrator Algorithms (SIA): numerical integrators designed for Hamiltonian systems. As it is well known, n degrees of freedom Hamiltonian systems have an important property: their ows preserve not only the total volume of the phase space, which is only one of the Poincaré invariants, but also the volume of sub-spaces less then 2n. These invariants are inherited from the conservation of the symplectic area. It is usually demanded of integrators that they should preserve energy. In this survey the main point is to convince the readers that the preservation of the symplectic area or canonicity of the Hamiltonian ow can be equally important, mainly when the concern is not one particular trajectory but the behavior of the phase space as a whole for long intervals of time. The KAM theorem asserts that for any integrable Hamiltonian perturbed by a small Hamiltonian term, such as that caused by the construction of the SIA, the perturbed dynamics preserves most of the incommensurate, nondegenerate, invariant tori. Unstable objects and their invariant manifolds are structurally stable and will be well represented by symplectic integrators.

Resumo em Inglês:

Chaotic magnetic field lines play an important role in plasma confinement by tokamaks. They can either be generated in the plasma as a result of natural instabilities or artifficially produced by external conductors, like resonant helical windings and ergodic magnetic limiters. This is a review of works carried out at the Universidade de São Paulo and Universidade Federal do Paraná on theoretical and experimental aspects of generation and control of chaotic magnetic field lines in tokamaks.