Resumo em Inglês:

The high-quality cosmological data, which became available in the last decade, have thrusted upon us a rather preposterous composition for the universe which poses one of the greatest challenges theoretical physics has ever faced: the so-called dark energy. By focusing our attention on specific examples of dark energy scenarios, we discuss three different candidates for this dark component, namely, a decaying vacuum energy or time-varying cosmological constant [lambda(tau)], a rolling homogeneous quintessence field (phi), and modifications in gravity due to extra spatial dimensions. As discussed, all these candidates [along with the vacuum energy or cosmological constant (lambda)] seem somewhat to be able to explain the current observational results, which hampers any definitive conclusion on the actual nature of the dark energy.

Resumo em Inglês:

We present the status and plans of the Angra Project, a new reactor neutrino oscillation experiment, proposed to be built in Brazil at the Angra dos Reis nuclear complex. This experiment is aimed to measure theta13, the last unknown of the three neutrino mixing angles. We propose a high sensitivity multi-detector experiment, able to reach a sensitivity to antineutrino disappearance down to sin² 2theta13 = 0.006 in a three years running period, by combining a high luminosity design, very low background from cosmic rays and careful control of systematic errors. We also intend to explore the possibility to use the neutrino detector for purposes of safeguards and non-proliferation of nuclear weapons.

Resumo em Inglês:

Cosmic microwave background (CMB) studies underpin our understanding of the universe and its history. Until recently, we have relied principally on CMB temperature observations to build our standard cosmological model, but today the field forges ahead into its next frontier - CMB polarization anistropy. Polarization measurements will furnish fresh and independent information on the primordial density perturbations and cosmological parameters, and they offer the exciting potential to detect primordial gravity waves, constrain dark energy and measure the neutrino mass scale. I review the science and long-term goals of CMB polarization measurements and discuss current results and future observational projects. A vigorous program of ground-based, suborbital and space-based (e.g., WMAP and Planck [2008]) experiments is guiding us towards a future space mission dedicated to high precision polarization measurements.

Resumo em Inglês:

In this talk I describe an interesting relation between Feynman graphs at finite temperature and chemical potential and the corresponding ones at zero temperature. The operator relating the two which we call the "thermal operator", simplifies the evaluation of finite temperature graphs and helps in understanding better several physical questions such as cutting rules, forward scattering, gauge invariance etc at finite temperature.

Resumo em Inglês:

We start this paper with a historical survey of the Casimir effect, showing that its origin is related to experiments on colloidal chemistry. We present two methods of computing Casimir forces, namely: the global method introduced by Casimir, based on the idea of zero-point energy of the quantum electromagnetic field, and a local one, which requires the computation of the energy-momentum stress tensor of the corresponding field. As explicit examples, we calculate the (standard) Casimir forces between two parallel and perfectly conducting plates and discuss the more involved problem of a scalar field submitted to Robin boundary conditions at two parallel plates. A few comments are made about recent experiments that undoubtedly confirm the existence of this effect. Finally, we briefly discuss a few topics which are either elaborations of the Casimir effect or topics that are related in some way to this effect as, for example, the influence of a magnetic field on the Casimir effect of charged fields, magnetic properties of a confined vacuum and radiation reaction forces on non-relativistic moving boundaries.

Resumo em Inglês:

We investigate the emergence of time-dependent nonperturbative configurations during the evolution of nonlinear scalar field models with symmetric and asymmetric double-well potentials. Complex spatio-temporal behavior emerges as the system seeks to establish equipartition after a fast quench. We show that fast quenches may dramatically modify the decay rate of metastable states in first order phase transitions. We discuss possible applications in condensed matter systems and in inflationary cosmology.

Resumo em Inglês:

Data taken with a radio antenna array in combination with the ground-level air shower experiment KASCADE-Grande at the Forschungszentrum Karlsruhe open up the possibility to measure large extensive air showers with this new technique. The pulse height of the observed radio signals scales with the primary energy of the particles initiating the air shower. The dependence of the radio signal on the angle of the shower axis with respect to the Earth's geomagnetic field and the coherence of the radiation suggest that the radio signal generation is due to the geosynchrotron mechanism.

Resumo em Inglês:

We consider the N-component tri-dimensional massive Gross-Neveu model at finite temperature and with compactified spatial coordinates. We study the behavior of the renormalized large-N effective coupling constant, investigating its dependence on the compactification length and the temperature. We show that spatial confinement exists for the model at T = 0, which is destroyed by raising the temperature.

Resumo em Inglês:

In this brief review we explicitly calculate the radiative corrections to the Chern-Simons-like term in the cases of zero and finite temperature, and in the gravity theory. Our results are obtained under the general guidance of dimensional regularization.

Resumo em Inglês:

In the last years, we experienced a complete change of the view of weak interaction physics. Robust results from many experiments as Super-Kamiokande, KamLAND, SNO, K2K, show us that the neutrinos have the remarkable phenomena of oscillations, a quantum interference mechanism that operates to distances as large as 100 km and even bigger distances. From this we know that neutrinos change identity from one flavor to another, as was demonstrated by the joints results of SNO and Super-Kamiokande experiments. We show here the review of latest results of neutrino physics, as for example, the first evidence of neutrinos produced in the core of the earth and the updated results of KamLAND and others. Our understating of all experimental results will completed by the state-of-art of the theoretical effort to understand such phenomena. For the near future, we expect the new generation of precision physics, like the running experiments of MINOS and Double CHOOZ, and the proposals of SADO and ANGRA shed light on unresolved issues such as the CP-violation for neutrinos and the relative magnitude of solar and atmospheric scales.

Resumo em Inglês:

We review in these notes the status of the construction of the Pierre Auger Observatory and present the first Physics results, based on the data collected during the first year and a half of operation. These results are preliminary, once the work to understand the systematics of the detectors are still underway. We discuss the cosmic ray spectrum above 3 EeV, based on the measurement done using the Surface Detector and the Fluorescence Detector, both, components of the observatory. We discuss, as well, the search for anisotropy near the Galactic Center and the limit on the photon fraction at the highest energies.

Resumo em Inglês:

In these proceedings, I shall review the basic concepts of perturbative QCD in its high-energy limit, emphasising the approach to the unitarity limit, usually referred to as saturation. I shall explain the basic framework showing the need for saturation, first, from a simple picture of the high-energy behaviour, then, giving a short derivation of the equation driving this evolution. In the second part, I shall exhibit an analogy with statistical physics and show how this allows to derive geometric scaling in QCD with saturation. I shall finally consider the effects of gluon-number fluctuations on this picture.

Resumo em Inglês:

The XXVI Encontro Nacional de Física de Partículas e Campos (ENFPC: Brazilian National Meeting on Particles and Fields) took place in São Lourenço, MG, Brazil, in October 2005. I was invited to deliver the summary talk on the area of gravitation and cosmology, in which I took the opportunity to briefly present a historic sketch of the ideas related to relativity, gravitation and cosmology in general, then some admittedly idiosyncratic highlights on current research in the field and an overview of some aspects of the corresponding national situation.

Resumo em Inglês:

I will compare the field theory works presented during the 2005 Encontro Nacional de Física de Partículas e Campos with what is done in the rest of the world in this area.

Resumo em Inglês:

Conducting polyaniline (PANI) has been synthesized using Sol-gel technique with chemical oxidation process. Chemically prepared cadmium sulphide has been printed on pellet of conducting polyaniline using screen-printing technique. I-V characteristics of conducting polyaniline and CdS printed conducting polyaniline have been recorded at room temperature using Keithley Electrometer. The results indicated that I-V of conducting polyaniline shows non-ohmic behaviour and I-V characteristic of CdS printed PANI, a CdS/ PANI heterojunction, shows the rectification effect and confirms that a diode can be fabricated by using simple technique.

Resumo em Inglês:

The binding energies as well as wave functions of hydrogenic impurities located in V-groove GaAs/Al xGa1-xAs quantum wires are calculated for different positions of the impurity inside the wires. The variational method is used and the carrier ground states are analytically calculated by an effective potential scheme together with a suitable coordinate transformation that allows the decoupling of the two-dimensional Schrodinger equation. The results are in good agreement with experimental points and other previous investigations.

Resumo em Inglês:

We studied the turbulent interactions among vertical wind velocity and temperature time-series measured in the Amazonian forest, during the wet season campaign of Large Biophere-Atmosphere Experiment in Amazonia (LBA) in 1999. The approach is based on the estimation of the correlation coefficient between the different scales in turbulent fields and Cross Wavelet Power (XWP). The results suggest that the correlations among scales of the vertical wind velocity are due to the Coherent Structures (CS), a large scale signature in the thermal profile. These coherent structures, kind of ramps, promoted an increase in the interaction among both variables, vertical wind velocity and temperature, and also depends on the atmospheric stability conditions. Furthermore, these coherent structures may explain the higher values of the correlation coefficient found in the large scales during the diurnal period compared with the nocturnal period, for the vertical wind velocity.

Resumo em Inglês:

We prove that a spherically symmetric solution of the field equations of the metric nonsymmetric theory of gravitation developed previously is necessarily static.This is the analogue of the well known Birkhoff theorem in general relativity.

Resumo em Inglês:

FRW models of the universe have been studied in the cosmological theory based on Lyra's manifold. A new class of exact solutions has been obtained by considering a time dependent displacement field for variable deceleration parameter from which three models of the universe are derived (i) exponential (ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these models of the universe are also discussed. Finally some possibilities of further problems and their investigations have been pointed out.

Resumo em Inglês:

The D*Dpi form factor is evaluated at low and moderate Q² in a hadronic loop model, for off-shell D mesons. The results contain arbitrary constants, which are fixed so as to match a previous QCD sum rule calculation valid at higher Q². The form factor obtained in this way is used to extract the coupling constant, which is in very good agreement with the experimental value.

Resumo em Inglês:

We apply a functional-integral formalism for Markovian birth and death processes to determine asymptotic corrections to mean-field theory in the Malthus-Verhulst process (MVP). Expanding about the stationary mean-field solution, we identify an expansion parameter that is small in the limit of large mean population, and derive a diagrammatic expansion in powers of this parameter. The series is evaluated to fifth order using computational enumeration of diagrams. Although the MVP has no stationary state, we obtain good agreement with the associated quasi-stationary values for the moments of the population size, provided the mean population size is not small. We compare our results with those of van Kampen's omega-expansion, and apply our method to the MVP with input, for which a stationary state does exist. We also devise a modified Fokker-Planck approach for this case.

Resumo em Inglês:

We present a comparative study carried out on the optical and electrical characteristics of undoped and Te doped AlGaAsSb/AlAsSb Bragg mirrors with 6.5 pairs of layers and bulk undoped and Te doped AlGaAsSb epilayers alloys lattice matched on InP, grown by molecular beam epitaxy, using SIMS, photoluminescence, reflectivity and IxV techniques. The temperature dependence of PL transitions observed in the Bragg mirrors are similar to that observed in bulk samples and associated with the donor and acceptor recombinations in alloys with electrostatic potential fluctuations described by quasi-donor-acceptor-pair (QDAP) models. We verified by SIMS the presence of a macro fluctuation in the Te profile concentrations in the growth direction of the doped Bragg mirror. The influence of doping, alloy and macrofluctuation of incorporated Te on the optical and electrical properties of doped Bragg mirror is analyzed. The AlGaAs/AlAsSb seems a very attractive option for VCSEL technology.

Resumo em Inglês:

The classical and relativistic Hamilton-Jacobi approach is applied to the one-dimensional homogeneous potential, V(q) = alphaq n, where alpha and n are continuously varying parameters. In the non-relativistic case, the exact analytical solution is determined in terms of alpha, n and the total energy E. It is also shown that the non-linear equation of motion can be linearized by constructing a hypergeometric differential equation for the inverse problem t(q). A variable transformation reducing the general problem to that one of a particle subjected to a linear force is also established. For any value of n, it leads to a simple harmonic oscillator if E > 0, an "anti-oscillator" if E < 0, or a free particle if E = 0. However, such a reduction is not possible in the relativistic case. For a bounded relativistic motion, the first order correction to the period is determined for any value of n. For n >> 1, it is found that the correction is just twice that one deduced for the simple harmonic oscillator (n = 2), and does not depend on the specific value of n.

Resumo em Inglês:

The first-principles molecular cluster discrete variational method (DV) is used to investigate the electronic structure and local magnetic properties of Cr impurities in bcc iron and Fe/Cr interfaces. The spin polarized case is considered within the framework of the local-spin-density approximation of the density function theory. The effect on the local moment and hyperfine magnetic field (Fermi contact term) of adding Cr atoms in the vicinity of Fe atoms is investigated. For a Cr impurity in bcc iron the calculated magnetic moment and hyperfine field is -0.62 µB and -300 kG, respectively. For pure chromium we obtained -0.49 µB and -67 kG. The Fe moment is sensitive to the separation between Cr atoms in the first shell of neighbors.

Resumo em Inglês:

We have proposed a semi-microscopic approach to calculate the two particles - two holes (2p - 2h) spreading width of giant resonances. Our proposal has been based in a hybrid method that implements the statistical multistep compound theory of Feshbach, Kerman and Koonin (FKK), widely and successful used in nuclear reactions mechanisms, in order to include relevant informations about the microscopic structure obtained by the Random Phase Approximation (RPA) calculations. This method is an approximative calculation to avoid the intrinsic numerical difficulties of those microscopic calculations that incorporate more complex structure than one particle - one hole (1p - 1h) excitations. Unlike the reaction context, the residual interaction was adjusted in RPA calculation to reproduce the lowest energy levels of the studied nuclei. The feasibility and the efficiency of the approach has been tested in giant dipole resonances in 208Pb and neutron-rich calcium isotopes, 48Ca and 60Ca.

Resumo em Inglês:

This work studies the pseudo-orbital SO(6) symmetry for the first half of the {2${\rm p}_{\frac{1}{2}}$}{2${\rm p}_{\frac{3}{2}}$}{1${\rm f}_{\frac{5}{2}}$} shell (denoted as the pf-shell). The spectra and beta decay are calculated for nuclei Ni, Cu and Zn with A=58, and the comparison to experiment prefers the \mbox{$\widetilde{\rm SO}(6)$} limit to the \mbox{$\widetilde{\rm SU}(3)$} one. In the calculation of beta decay two types of transformations are employed and the results seem confirm the adequacy of p-helicity transformation.

Resumo em Inglês:

Second harmonic generation (SHG) in nonlinear optical crystal is well-established technique for the measurement of the pulse-width of ultrafast femtosecond laser pulses. However, only selected nonlinear crystalline materials are suited for this purpose due to the limitations in transparency cut-off, limited phase-matching wavelength range, and large difference between the group velocities of the fundamental and harmonic waves. It is found that some newly discovered crystals, such as CsLiB6O10 (CLBO), K2Al2B2O7 (KABO), Li2B4O7 (LB4), and KBe2BO3F (KBBF) have some advantageous characteristics for use in ultrafast nonlinear optical applications. Here we have presented several linear and nonlinear optical parameters including phase-matching angle, angular and spectral acceptance bandwidths, walk-off angle, nonlinear coupling coefficient, and group-velocity mismatch for generation of second harmonic of ultrafast laser radiations by employing type-I and type-II SHG techniques in these crystals.

Resumo em Inglês:

We study the entropy production in nonequilibrium systems described by a Fokker-Planck equation. We have devised an expression for the entropy flux in the stationary state. We have found that the entropy flux can be written as an ensemble average of an expression containing the force and its derivative. This result is similar to the one used by Lebowitz and Spohn for system following a Markovian process in discrete space. We have also been able to obtain a fluctuation-dissipation type relation between the dissipated power, which was written as an ensemble average, and the production of entropy for the case of systems in contact with one heat bath. We have applied the results for a simple model for particles subjected to dissipative forces.

Resumo em Inglês:

New examples of the theory recently proposed by Ricca [PRA(1991)] on the generalization of Da Rios-Betchov intrinsic equations on curvature and torsion of classical non-Riemannian vortex higher-dimensional string are given. In particular we consider applications to 3-dimesional fluid dynamics, including the case of a twisted flux tube and the fluid rotation. In this case use is made of Da Rios equation to constrain the fluid. Integrals on the Cartan connection are shown to be related to the integrals which represent the total Frenet torsion and total curvature. By analogy with the blue phases twisted tubes in liquid crystals, non-Riemannian geometrical formulation of the twisted flux tube in fluid dynamics is obtained. A theorem by Ricca and Moffatt on invariant integrals for the Frenet curvature is used to place limits on the Cartan integrals. The stationary incompressible flow case is also addressed in the non-Riemannian case where Cartan torsion scalars are shown to correspond to abnormalities of the congruence. Geodesic motion is shown to be torsionless. Vorticity is shown to be expressed in terms of abnormalities of the congruence, which is analogous to the result recenly obtained [Garcia de Andrade,PRD(2004)], where the vorticity of the superfluid plays the role of Cartan contortion vector in the context of analog gravity.

Resumo em Inglês:

We study the nonlinear magnetic excitation in an anisotropic ferromagnet with a magnetic field. In the long wave approximation, the Landau-Lifschitz equation with easy axis anisotropy is transformed into the nonlinear Schrödinger type. By means of a straightforward Darboux transformation we obtain the one- and two-soliton solutions of uniaxial anisotropic ferromagnet. From a careful analysis for the asymptotic behavior of two-soliton solution we find that the collision between two magnetic solitons is elastic. This will be very helpful to understand the significant nature of the interactions between solitons in the future.

Resumo em Inglês:

Franck-Condon factors (vibrational transition probabilities) and r-centroids have been evaluated by a numerical integration procedure for the bands of A 0+g - X ¹sigma+, B 0+g - X ¹sigma+ systems of AuH and A 0+ - X ¹sigma+ system of AuD molecules using a suitable potential. The physical and astrophysical significances of our evaluated Franck-Condon factors and r-centroids have also been discussed, which would be helpful in the prediction of the presence of AuH and AuD molecules in various celestial bodies.

Resumo em Inglês:

The Symplectic Projector Method is applied to derive the local physical degrees of freedom and the physical Hamiltonian of the Maxwell-Chern-Simons theory in d = 1+2. The results agree with the ones obtained in the literature through different approaches.

Resumo em Inglês:

This paper is devoted to a review of recent progresses concerning the computation of the Casimir force between two parallel plates delimitating a polymer blend or a ternary polymer solution (with a good solvent). We assume that, close to the consolute point, one or the two polymers of the mixture are strongly attracted by the plates (critical adsorption). For both systems, the induced force originates from the fluctuations of composition near the consolute point. In polymer blends case, it was found that the force decreases with separation L between the two plates as L-4, with a known universal amplitude. For ternary polymer solutions, however, it has been shown that the interaction force decays rather as L-3. This drastic change of the force expression is due to the presence of the good solvent, which gives rise to additional fluctuations of polymer concentration. To do calculations, for the two systems, use is made of the standard sigma4-theory, where the field sigma is the order parameter or composition fluctuation.

Resumo em Inglês:

This paper is the outgrowth of lectures the author gave at the Physics Institute and the Chemistry Institute of the University of São Paulo at São Carlos, Brazil, and at the VIII'th Summer School on Electronic Structure of the Brazilian Physical Society. It is an attempt to introduce density-functional theory (DFT) in a language accessible for students entering the field or researchers from other fields. It is not meant to be a scholarly review of DFT, but rather an informal guide to its conceptual basis and some recent developments and advances. The Hohenberg-Kohn theorem and the Kohn-Sham equations are discussed in some detail. Approximate density functionals, selected aspects of applications of DFT, and a variety of extensions of standard DFT are also discussed, albeit in less detail. Throughout it is attempted to provide a balanced treatment of aspects that are relevant for chemistry and aspects relevant for physics, but with a strong bias towards conceptual foundations. The paper is intended to be read before (or in parallel with) one of the many excellent more technical reviews available in the literature.