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Brazilian Journal of Physics, Volume: 31, Número: 2, Publicado: 2001
  • XXIst Brazilian National Meeting on Particles and Fields: FOREWORD

  • High Density QCD

    Gay Ducati, M.B.

    Resumo em Inglês:

    The dynamics of high partonic density QCD is presented considering, in the double logarithm approximation, the parton recombination mechanism built in the AGL formalism, developed including unitarity corrections for the nucleon as well for nucleus. It is shown that these corrections are under theoretical control. The resulting non linear evolution equation is solved in the asymptotic regime, and a comprehensive phenomenology concerning Deep Inelastic Scattering like F2, F L, F<img SRC="http:/img/fbpe/bjp/v31n2/02eq43.gif">. <FONT FACE=Symbol>¶</FONT>F2 / <FONT FACE=Symbol>¶</FONT>ln Q², <FONT FACE=Symbol>¶</FONT>F<img SRC="http:/img/fbpe/bjp/v31n2/02eq44.gif"> / <FONT FACE=Symbol>¶</FONT>ln Q², etc, is presented. The connection of our formalism with the DGLAP and BFKL dynamics, and with other perurbative (K) and non perturbative (MV-JKLW) approaches is analised in detail. The phenomena of saturation due to shadowing corrections and the relevance of this effect in ion physics and heavy quark production is emphasized. The implications to e-RHIC, HERA-A, and LHC physics and some open questions are mentioned.
  • Frontiers of Inflationary Cosmology

    Brandenberger, Robert H.

    Resumo em Inglês:

    After a brief review the theory of cosmological perturbations, I highlight some recent progress in the area of reheating in inflationary cosmology, focusing in particular on parametric amplification of super-Hubble cosmological fluctuations, and on the role of noise in the resonance dynamics (yielding a new proof of Anderson localization). I then discuss several important conceptual problems for the current realizations of inflation based on fundamental scalar matter fields, and review some new approaches at solving these problems.
  • CP Violation: Past, Present, and Future

    Rosner, Jonathan L.

    Resumo em Inglês:

    We discuss the history of CP violation and its manifestations in kaon physics, its explanation in terms of phases of the Cabibbo-Kobayashi-Maskawa matrix describing charge-changing weak quark transitions, predictions for experiments involving B mesons, and the light it can shed on physics beyond the Standard Model.
  • Finite Temperature and Large Gauge Invariance

    Das, Ashok

    Resumo em Inglês:

    In this talk, I will sumarize the status of our understanding of the puzzle of large gauge invariance at finite temperature.
  • Non Relativistic Limit in QFT: a Wilson Renormalization Group Approach in the Minkowski Space

    Silva, A.J. da

    Resumo em Inglês:

    We study the non relativistic limit of a model of fermions interacting through a Chern-Simons field, from a perspective that resembles the Wilson Renormalization Group (WRG) approach. The main difference of our approach to WRG is that instead of working in the Euclidean space, we directly work in Minkowski space. For the nonrelativistic limit this procedure admits a more direct interpretation of the results. As we will see, this modified WRG approach solves some difficulties, and gives a new understanding of non relativistic models that are not clear in the usual "classical" nonrelativistic (CNR) limit found in most text books. The method is general and our choice of the Chern-Simons as the gauge field is only for the sake of simplicity of illustration.
  • The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Proton

    Krein, G.

    Resumo em Inglês:

    We present an overview of the present theoretical status of the Gerasimov-Drell-Hearn (GDH) sum rule. It is emphasized the importance of near threshold s-wave photoproduction contributions to the sum rule. We also discuss the experimental verification of the sum rule, with particular emphasis on the recent experiment at the Mainz Microtron (MAMI). The spin polarizabilities and the generalized GDH sum rule, which are of interest to issues related to the spin of the proton as measured at high energies, are discussed.
  • Dark Matter in the Universe

    Opher, Reuven

    Resumo em Inglês:

    We treat here the problem of dark matter in galaxies. Recent articles seem to imply that we are entering into the precision era of cosmology, implying that all of the basic physics of cosmology is known. However, we show here that recent observations question the pillar of the standard model: the presence of nonbaryonic "dark matter" in galaxies. Using Newton's law of gravitation, observations indicate that most of the matter in galaxies is invisible or dark. From the observed abundances of light elements, dark matter in galaxies must be primarily nonbaryonic. The standard model and its problems in explaining nonbaryonic dark matter will first be discussed. This will be followed by a discussion of a modification of Newton's law of gravitation to explain dark matter in galaxies.
  • Critical Phenomena in Gravitational Collapse: The Studies So Far

    Wang, Anzhong

    Resumo em Inglês:

    Studies of black hole formation from gravitational collapse have revealed interesting non-linear phenomena at the threshold of black hole formation. In particular, in 1993 Choptuik studied the collapse of a massless scalar field with spherical symmetry and found some behaviour, which is quite similar to the critical phenomena well-known in Statistical Mechanics and Quantum Field Theory. Universality and echoing of the critical solution and power-law scaling of the black hole masses have given rise to the name Critical Phenomena in Gravitational Collapse. Choptuik's results were soon confirmed both numerically and semi-analytically, and have extended to various other matter fields. In this paper, we shall give a brief introduction to this fascinating and relatively new area, and provide an updated publication list. An analytical "toy" model of critical collapse is presented, and some current investigations are given.
  • Critical Behavior of High Temperature Superconductors

    Calan, Claude de

    Resumo em Inglês:

    We consider the scaling behavior in the critical domain of superconductors at zero external magnetic field. The Josephson's relation for a charged superfluid is proved without assuming the hyperscaling relation. On the other hand we discuss the dual Ginzburg-Landau model. In this dual model, due to the presence of two mass scales, a continuous family of non equivalent scalings can be defined. The relevant critical regimes are identified, and the corresponding critical exponents are predicted.
  • Low Energy (Anti)atoms for Precision Tests of Basic Physics

    Silveira, D.M.; Pereira, O.; Veloso, M.; Cesar, Claudio L.

    Resumo em Inglês:

    Recent advances in techniques to manipulate and study, with high precision, atomic hydrogen, from one hand, and successful trapping schemes for positrons and antiprotons, from the other hand, have encouraged the pursuit of experiments to test CPT violation and the Weak Equivalence Principle (WEP) through the comparison of hydrogen and antihydrogen. A description of the hydrogen trap and laser system being built in Rio, to trap and perform high resolution spectroscopy on cold hydrogen, is presented along with a discussion on the techniques and experimental system being implemented by the ATHENA collaboration at CERN to produce cold antihydrogen. A new technique to make a cold antihydrogen beam is proposed.
  • Physics in the Global Monopole Spacetime

    Bezerra de Mello, E.R.

    Resumo em Inglês:

    In this paper we review some important aspects of the global monopole spacetime and present how this manifold modifies, at classical and quantum points of view, the movement of a charged particle. The explicit calculations of the renormalized vacuum expectation values of the energy-momentum tensors, <FONT FACE=Symbol>á</FONT>T<FONT FACE=Symbol>mn</FONT>(x)<FONT FACE=Symbol>ñ</FONT>Ren., associated with massless bosonic and fermionic fields are also presented. Moreover the effect of the nonzero temperature in this previous formalism is analyzed. Finally, we briefly present other applications of this manifold in the topological inflation and condensed matter system.
  • Searches at LEP2 Latest Results

    Begalli, M.

    Resumo em Inglês:

    Searches for the Higgs boson of the Standard Model and supersymmetric models have been performed by the four LEP experiments in the data collected over almost 12 years (August/1989 until November/2000) at centre-of-mass energies varying from 91.2 GeV to 209 GeV. An excess of candidates for the process e+e<FONT FACE=Symbol>- ®</FONT> Z*<FONT FACE=Symbol>®</FONT> Z0<FONT FACE=Symbol></FONT>H0 was found for Higgs masses near 114 GeV.
  • Electromagnetic Duality, Charges, Monopoles, Topology, ...

    Mignaco, Juan A.

    Resumo em Inglês:

    In this talk we review the subject of electromagnetic duality, and related ones, as "normal" electric and magnetic charges, being different from monopoles (magnetic or electric), the topological content of monopoles, surface terms, Dirac strings and chiral structure in the inclusion of massless spinor field and its relation to torsion. We limit our discussion to the simplest, Heaviside electromagnetic duality, include some links with the nonabelian gauge theories and make no comment on the use of this concept in string theories. Old and recent contributions on the subject are presented and discussed, and possible lines of research will hopefully be indicated.
  • Cosmic Accelerators and Terrestrial Detectors

    Shellard, Ronald Cintra

    Resumo em Inglês:

    We review the status of ultrahigh energy cosmic rays studies, discussing the mechanisms for their production and propagation through space. We look into the strategy to measure those events and describe a new observatory, which is in construction, to observe those particles, the Pierre Auger Observatory.
  • Noncommutative Supersymmetric Field Theories

    Rivelles, Victor O.

    Resumo em Inglês:

    We discuss some properties of noncommutative supersymmetric field theories which do not involve gauge fields. We concentrate on the renormalizability issue of these theories.
  • Exotic Solutions to the Solar Neutrino Anomaly

    Guzzo, M. M.

    Resumo em Inglês:

    We analyze the status of the exotic solutions to the solar neutrino problem, i.e., those solutions based on new phenomena which are not the usual neutrino oscillations induced by masses and mixing. These solutions are based on different assumptions: a) resonant spin-flavor precession induced by non-vanishing neutrino magnetic moment, b) the existence of non-standard flavor-changing and non-universal neutrino interactions and c) the violation of the equivalence principle. We investigate the quality of the fit provided by each one of these solutions not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration.
  • Remarks on Topological Models and Fractional Statistics

    Almeida, C.A.S.

    Resumo em Inglês:

    One of the most intriguing aspects of Chern-Simons-type topological models is the fractional statistics of point particles which has been shown essential for our understanding of the fractional quantum Hall effects. Furthermore these ideas are applied to the study of high Tc superconductivity. We present here an recently proposed model for fractional spin with the Pauli term. On the other hand, in D=4 space-time, a Schwarz-type topological gauge theory with antisymmetric tensor gauge field, namely B ^ F model, is reviewed. Antisymmetric tensor fields are conjectured as mediator of string interaction. A dimensional reduction of the previous model provides a (2+1) dimensional topological theory, which involves a 2-form B and a 0-form phi. Some recent results on this model are reported. Recently, there have been thoughts of generalizing unusual statistics to extended objects in others space-time dimensions, and in particular to the case of strings in four dimensions. In this context, discussions about fractional spin and antisymmetric tensor field are presented.
  • Summary Talk: Cosmology and Gravitation

    Waga, Ioav

    Resumo em Inglês:

    The works on Cosmology and Gravitation presented during the XXI Brazilian National Meeting on Particle and Fields (BNMPF) are brie y reviewed.
  • Summary Talk: Particle Physics Phenomenology

    Ferreira, Erasmo

    Resumo em Inglês:

    We summarize the contributed papers and the talks in the plenary and parallel sessions in this XXI Brazilian National Meeting on Particles and Fields that are classified as of phenomenology kind. We try to put the activities here developed in the perspective of the existing community of phenomenologists in Brazil 2000.
  • Summary Talk: Experimental High Energy Physics

    Anjos, J. C.

    Resumo em Inglês:

    A summary of the contributions on Experimental High Energy Physics at the XXI Brazilian National Meeting on Particle and Fields is presented. There were a total of 28 contributions, 21 in Panel Sessions and 7 in Oral Sessions.
  • Summary Talk: Field Theory

    Gomes, M.

    Resumo em Inglês:

    We present some remarks on the works reported at the section of particles and fields of the XXI Brazilian National Meeting on Particles and Fields.
  • Analysis of SiO2 Thin Films Deposited by PECVD Using an Oxygen-TEOS-Argon Mixture Regular Articles

    Viana, Carlos E.; Silva, Ana N. R. da; Morimoto, Nilton I.; Bonnaud, Olivier

    Resumo em Inglês:

    This study analyses the influence of the argon flow on the Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon oxide thin films by using TEOS as silicon source. The argon flow increases the deposition rate, however it also can creates some defects in the deposited film. Several characterization techniques were used to analyze the deposited films. The presence of argon, in the gas phase, modifies the plasma composition, the surface roughness of silicon wafer, and the surface reaction. The optimum argon flow ranges between 65 and 80 sccm to obtain a silicon oxide thin film with high quality in terms of refractive index, smoothness, and uniformity.
  • Vector Constants of Motion for Time-Dependent Kepler and Isotropic Harmonic Oscillator Potentials Regular Articles

    Ritter, O.M.; Santos, F.C.; Tort, A. C.

    Resumo em Inglês:

    We discuss a method for obtaining vector constants of motion for time-dependent central fields.
  • Images by Nuclear Magnetic Resonance: A Modified Version of the EPI Method Regular Articles

    Ramalho, Simone Souza; Borges, Nilson Mendes; Wolney Filho, Waldemar

    Resumo em Inglês:

    It is well known that data accquisition times and image reconstruction procedures in conventional magnetic resonance imaging (MRI) are usually long. For time dependent phenomena, such as sample motion, respiration, blood flow pulsation and others, faster accquision times are desirable to avoid ghosting artifacts. Over the last two decades, a great number of fast and ultra-fast MRI methods have been proposed that greatly reduce the accquision times. One of them is the echo-planar imaging (EPI) method which uses a single excitation scheme to scan entirely the k-space in a very short time. In the initial sections of this work we will supply the reader with a brief description of the image reconstruction procedures for the conventional MRI sequence and four different schemes of the EPI method. However, our main objective is to propose a modified version of the spin-echo EPI method, suggesting a sequence with the use of a constant phase encoding gradient.
  • Note on BEC in Nonextensive Statistical Mechanics Regular Articles

    Fa, Kwok Sau; Lenzi, E. K.

    Resumo em Inglês:

    The generalized Bose-Einstein distribution, within the dilute gas assumption, in the nonextensive Tsallis statistics is worked without approximation for the Bose-Einstein condensation (BEC). The results obtained are compared with the recent results presented in Int. J. Mod. Phys. B 14, 405 (2000) by L. Salasnich. Furthermore, in order to promote a complete analysis for the BEC in the nonextensive scenario we also find exact expression within the normalized constraints in a harmonic trap.
  • Gaussian Basis Sets for the Calculation of Some States of the Lanthanides Regular Articles

    Librelon, P.R.; Jorge, F.E.

    Resumo em Inglês:

    Highly accurate adapted Gaussian basis sets are used to study the ground and some excited states for the neutral atoms and also some corresponding 6s and 4f ionized states from Cs through Lu. Our total energies are compared with those calculated with a numerical Hartree-Fock method. The mean error of our energy results is equal to 0.74 mhartree. Our calculations reproduce the experimental trend to increase or to decrease the 6s and 4f ionization potentials with increasing atomic number, although they are respectively smaller and larger than the experimental values.
  • Analysis of the Ratio of (p, pn) to (p, 2p) Reaction Cross Sections Regular Articles

    Shostak, V.B.; Palkin, G.P.; Woloshin, N.I.; Likhachev, V.P.; Arruda-Neto, J.D.T.; Cruz, M.T.F. da; Martins, M.N.

    Resumo em Inglês:

    The ratio of the differential cross sections for the reactions 7 Li(p, 2p)6 He and 7 Li(p, pn)6 Li, at incident proton energy of 70 MeV, were analyzed in the framework of DWT approach. FSI and off-shell contributions were factorized and compared with appropriate experimental data.
  • The Hierarchy of Hamiltonians for a Restricted Class of Natanzon Potentials Regular Articles

    Drigo Filho, Elso; Ricotta, Regina Maria

    Resumo em Inglês:

    The restricted class of Natanzon potentials with two free parameters is studied within the context of Supersymmetric Quantum Mechanics. The hierarchy of Hamiltonians and a general form for the superpotential is presented. The first members of the superfamily are explicitly evaluated.
  • Juan Alberto Mignaco (1940-2001) Obituary

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