Repositório RCAAP

We review some recent developments on BPS string solutions and monopole confinement in the Higgs (or color) superconducting phase of <IMG SRC="/img/revistas/bjp/v34n4a/caln_mai.gif" > or = 2 and <IMG SRC="/img/revistas/bjp/v34n4a/caln_mai.gif" > or = 4 super Yang-Mills theories. In particular, the monopole magnetic fluxes are shown to be always integer linear combinations of string fluxes. Moreover, a bound for the threshold length of the string breaking is obtained. When the gauge group SU(N) is broken to Z N, the BPS string tension satisfies the Casimir scaling law. Furthermore, in the SU(3) case the string solutions are such that they allow the formation of a confining system with three monopoles.

We review some conceptual problems in quantum field theory, with an emphasis on exact results and open problems.

I review different approaches to the construction of vortex and instanton solutions in noncommutative field theories.

Questions such as whether we live in a spatially finite universe, and what its shape and size may be, are among the fundamental open problems that high precision modern cosmology needs to resolve. These questions go beyond the scope of general relativity (GR), since as a (local) metrical theory GR leaves the global topology of the universe undetermined. Despite our present-day inability to predict the topology of the universe, given the wealth of increasingly accurate astro-cosmological observations it is expected that we should be able to detect it. An overview of basic features of cosmic topology, the main methods for its detection, and observational constraints on detectability are briefly presented. Recent theoretical and observational results related to cosmic topology are also discussed.

Analogue models of general relativity have recently been considered with great interest by the scientific community. They connect branches of physics as different as gravitation, condensed matter physics, electrodynamics, acoustics, and quantum field theory. One of the main expectations about such models lies on the possibility of testing in laboratory some aspects of quantum field theory in curved spacetimes. For instance, it seems to be possible to probe the existence of Hawking radiation by means of analogue models in the context of certain condensed matter systems. We briefly report the present day status of this topic of research. Some specific models are considered, particularly those presenting analogue event horizons as solutions. The issue of thermal emission (analogue Hawking radiation) is also discussed.

Teleparallel gravity can be seen as a gauge theory for the translation group. As such, its fundamental field is neither the tetrad nor the metric, but a gauge potential assuming values in the Lie algebra of the translation group. This gauge character makes of teleparallel gravity, despite its equivalence to general relativity, a rather peculiar theory. A first important point is that it does not rely on the universality of free fall, and consequently does not require the equivalence principle to describe the gravitational interaction. Another peculiarity is its similarity with Maxwell's theory, which allows an Abelian nonintegrable phase factor approach, and consequently a global formulation for gravitation. Application of these concepts to the motion of spinless particles, as well as to the COW and gravitational Aharonov-Bohm effects are presented and discussed.

Following the recent realization by the worldwide high energy physics community for the need of a next generation e+ e- collisions machine, we review the main reasons for such a proposal, and the current status of that endeavor. General aspects of the physics program, the collider itself, and its detectors are covered.

The Pierre Auger Observatory is a large international effort to provide measurements of extensive air showers (EAS) initiated in the upper atmosphere by cosmic rays with energies above 10(18) eV , the Ultra High Energy Cosmic Rays (UHECR's). The explanations for the origin, acceleration processes and composition of the UHECR's face theoretical and experimental difficulties, due to the extremely low flux in this energy region. The full observatory will consist of a hybrid detector using an array of 1600 water <IMG SRC="/img/revistas/bjp/v34n4a/a16img01.gif">erenkov tanks spread over an area of 3000 km² overlooked by a set of 4 air fluorescence detectors per site. The southern site is being instrumented in Argentina and I will discuss its present status in this paper.

We make a direct and model-independent measurement of the low pi+ pi- mass phase motion in the D+ <FONT FACE=Symbol>® p</FONT>-pi+pi+ decay. Our preliminary results show a strong phase variation, compatible with the isoscalar sigma(500) meson. This result confirms our previous result [1] where we found evidence for the existence of this scalar particle using full Dalitz-plot analysis. We apply the Amplitude Difference (AD) method [2] to the same Fermilab E791 data sample used in the preceding analysis. We also give an example of how we extract the phase motion of the scalar amplitude, looking at the f0(980) in Ds+ <FONT FACE=Symbol>® p</FONT>-pi+pi+ decay.

The high parton density regime of Quantum Chromodynamics (QCD) is briefly discussed. Some phenomenological aspects of saturation are described, mainly focusing on possible signatures of the non-linear QCD dynamics in electron-proton/nucleus collisions. Implications of these effects in central and ultraperipheral heavy-ion collisions are also presented.

The first KamLAND results are in a very good agreement with the predictions made on the basis of the solar neutrino data and the LMA realization of the MSW mechanism. We perform a combined analysis of the KamLAND (rate, spectrum) and the solar neutrino data with a free boron neutrino flux fB. The best fit values of neutrino parameters are deltam² = 7.1.10-5 eV², tan² theta = 0.40 and fB = 1.04 with the 1sigma intervals: deltam² = (6.4 - 8.4). 10-5 eV², tan² theta = 0.33 - 0.48. We find the 3sigma upper bounds: deltam² < 1.7 . 10-4 eV² and tan² theta< 0.64, and the lower bound deltam² > 4.8 . 10-5 eV². In the best fit point we predict for SNO: CC/NC = <IMG SRC="/img/revistas/bjp/v34n4a/a19img01.gif">and <IMG SRC="/img/revistas/bjp/v34n4a/a19img02.gif" > or = 3.0 ± 0.8% (68% C.L.), and <IMG SRC="/img/revistas/bjp/v34n4a/a19img02.gif">< 6% at the 3sigma level. Further improvements in the determination of the oscillation parameters are discussed and implications of the solar neutrino and KamLAND results are considered.

It is generally accepted that the LHC is the accelerator facility at which weak scale supersymmetry will either be discovered or definitely excluded. I give a brief introduction to weak scale supersymmetry presenting the general argument that limit the supersymmetrical spectrum to be below TeV energies. We will see that the LHC is able to search for supersymmetry in several of its realization far above the expected spectrum masses. However, in the last section we will see some well motivated scenarios where supersymmetric sparticles might be very heavy, thus beyond the LHC reach. Such scenarios deserve a more detailed study to push the LHC reach.

Past studies of neutrinos and the recent results on neutrino mixing have opened up many new possibilities as well as the understanding that neutrino mixing is very different from the better known quark mixing. The last remaining unmeasured component of the neutrino mixing matrix (Ue3) also provides a window to understanding neutrino matter effects, the mass hierarchy, and the possibility of measuring leptonic CP violation. A discussion of the benefits and difficulties of pursuing such a measurement with reactor neutrinos will be presented. In addition, possible sites for such an experiment will be discussed, including a location in Brazil.

In this paper we study the local persistence of the two-dimensional Blume-Capel Model by extending the concept of Glauber dynamics. We verify that for any value of the ratio alpha = D/J between anisotropy D and exchange J the persistence shows a power law behavior. In particular for alpha < 0 we find a persistence exponent thetal = 0:2096(13), i.e. in the Ising universality class. For alpha > 0 (<FONT FACE=Symbol>a ¹</FONT> 1) we observe the occurrence of blocking.

Coherent emission efficiency in a 100Å GaAs SQW microcavity was enhanced one order when pumped resonantly at 10 K, compared to the off-resonant excitation. The usual kink observed in the exciton emission linewidth as well as in the emission intensity in relation to the pump power, changes smoothly instead of the usual abrupt kink observed in the off-resonant microcavity laser. In addition, polarization measurements show a correlation relationship between the pump light polarization and the cavity emission polarization.

The possibility of quasi-stable trapping of charged particles of hundreds keV to MeV energy on the frontside Earth magnetosphere is explored in by numerical modeling of the single particle orbits in the geomagnetic field utilizing empirical Tsyganenko magnetic field model. Due to solar wind pressure the remote magnetic field lines on the frontside of the magnetosphere exhibit two minima in the geomagnetic field strength along the field line in high latitudes on the both sides of the equator. These minima may result in stable confinement structures, a kind of radiation belts, in the northern or/and the southern hemispheres, providing energetic particle trapping for times from several minutes to duration of seasonal scale. Simulation of energetic proton orbits passing through the regions of the magnetic field minima with different disturbance level and the Earth's tilt reveals conditions in which these trapped radiation zones could result. It is shown that the existence of the adiabatic confinement zones strongly depends on the seasonal inclination of the Earth's rotation axis. As a result the northern cusp confinement zone appears only in a summer solstice and similarly the southern cusp capture zone appears only in a winter solstice. In equinox time the confinement zones exist in both hemispheres in the disturbed magnetospheric conditions, however, they are less pronounced. The zones are essentially restricted to the sunlit magnetosphere. They form a kind of cusp radiation ring/belt, where a proton drifts with a period of several minutes, conserving its 1st and the 2nd adiabatic invariants. The latitudinal width of the ring is very thin, about 2-5 latitudinal degrees. The proton orbits passing through the off-equatorial field minimum opposite to those cusp belts reveal another interesting effect: a bound of the geomagnetic equatorial plane on the day sector. These and other features of the confinement zones in the two minima off-equatorial magnetic field regions are discussed.

Both Bose-Einstein condensates and optical fields are composed of bosons, so that the majority of the processes which have long been studied in quantum and nonlinear optics have equivalents in the field of Bose-Einsten condensation. However, due to the masses of the condensed atoms, the confining potentials and the huge collisional nonlinearities, the simpler theoretical approaches common to quantum optics can sometimes give misleading answers when applied to condensates. In this work we describe some of the areas where simplified treatments can be misleading, and compare and contrast the predictions of quantum many-body treatments with those of the single-mode type treatments which have been so successful in quantum optics.

We have measured the collisional loss rate for cold strontium atoms held in a magneto-optical trap as a function of light intensity in the regime of low intensity (2-6 mW/cm²). The results confirm our recently proposed model, where we showed that the sudden increase of loss rate at low intensities does not depend on hyperfine structure changing collision only. The model, which is based on radiative escape mechanism and a light intensity dependent escape velocity, is able to reproduce quite well the behavior of the experimental observations. The data here reported may be of importance for a recent proposed application for cold trapped 88Sr atoms, as well as other trappable alkaline earth metal atoms such as Ca.

Measurements on the ion flux transmission in a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with water-cooled electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. It is employed a Copper cathode (6 cm in diameter) with a Copper annular anode. The filter consists in a steel cylinder 500 mm length and 100 mm inner diameter with 90o of bending angle and corrugated lateral walls, surrounded by a magnetic field generating coil. The arc is operated at a current level of 100 A, and the intensity of the filtering magnetic field was in the range 0¡200 G (measured at the knee of the filter). This magnetic field is enough high so as to magnetize the electrons but not the ions. The discharge is ignited by bringing (and later removing) a tungsten striker into contact with the cathode. The arc voltage drop, the floating potentials of the filter and the plasma, and the ion current collected by probes located at different positions as functions of the magnetic field intensity are reported and compared with measurements presented in the literature with other similar devices.

An experimental characterization of a low-current (30-40 A) cutting torch is presented. To avoid contamination of the plasma arc by removed anode material, a rotating steel cylinder was used as the anode and the arc was anchored onto the cylinder lateral surface. The cathode-anode and cathode-nozzle voltage drops, together with the gas pressure in the plenum chamber were registered for different values of the mass flow rate injected into the plenum chamber. By employing an optical system with a large magnifi cation (<FONT FACE=Symbol>»</FONT> 15 X), the arc radius the nozzle exit was also determined with a digital optical camera. The obtained experimental quantities were used to evaluate several flow properties at the nozzle exit (hot arc plasma and cold gas temperatures, arc and gaz velocities, etc.) by employing a simplifi ed theoretical model for the plasma flow in the nozzle. The obtained results are in reasonable agreement with the data reported in the literature by other authors. Explanations of the origin of the clogging effect and the nozzle voltage are also presented.