Gauge fixing of Chern-Simons <Emphasis Type="Italic">N</Emphasis>-extended supergravity

We treat N-extended supergravity in 2 + 1 space-time dimensions as a Yang-Mills gauge field with Chern-Simons action associated to the N-extended Poincaré supergroup. We fix the gauge of this theory within the Batalin-Vilkovisky scheme.Received: 26 January 2004, Published online: 25 June 2004W. Spalenza: Supported in part by the Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq, Brazil     

Composition and magnetic properties of Fe/Fe x N thin film multilayers

The structure, composition, and magnetic characteristics of thin films multilayers of iron-iron nitride with high magnetic moment and very low coercive field are investigated. The present study together with previous ones that described in detail the magnetic properties lead to the establishment of certain requirements to obtain iron-iron nitride multilayers with outstanding magnetic characteristics.Supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil)     

On the perturbed angular correlation attenuation factor for relaxing systems

The attenuation factor of gamma-gamma perturbed angular correlation in the isotropic random-phase approximation is deduced for an axially symmetric quadrupole interaction and spins 1, 3/2, 2 and 5/2. It is shown that modifications to the usual expression are significant. Useful expressions for fitting procedures are obtained.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Financiadora de estudos e Projetos (FINEP).     

57Fe Mössbauer study in the ternary hydrides of ErFe3

The ternary hydride phases ErFe₃Hx (with x=1.5 and 2.7) has been studied by⁵⁷Fe Mössbauer effect. The spectra show that the spin reorientation temperature is increased by the presence of hydrogen in the ErFe₃ lattice and is independent of hydrogen concentration for the two hydrides investigated. A preferential filling of the interstitial sites in the RFe₃ structure is indicated by the data.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP).     

New NH2H4 far-infrared laser lines and their frequencies

We report 25 new far-infrared laser lines and 26 heterodyne frequency measurements in hydrazine. The frequencies range from 1.0 to 5.5 THz with most of the frequencies between 2.5 and 4.0 THz. The lines were generated in a high frequency, far-infrared Fabry-Perot laser cavity pumped by a CO₂ laser. The cavity has a high Q for wavelengths below 150 µm and uses variable coupling to optimize the power for each line.This work has been financed by the Brazilian Government - Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and by the United States Government - NASA grant W-18, 623.Contribution of NIST, not subject to U.S. copyright.     

The instrumental complexity of states

We apply a formalism developed previously to study the notion of the complexity of states in a general statistical theory. We identify the extreme points of the instrument sets as those instruments that view an intrinsic complexity of states and are uncontaminated by stochastic contributions of the experimenter. Various notions of entropy of a state are investigated.This work was financially supported by CNP_q (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and FINEP (Financiadora de Estudos e Projetos) of the Brazilian government.     

Frequency measurements of 3 to 11 THz laser lines of CH3OH

We measured the frequencies of 12 far-infrared laser lines generated in a high- frequency Fabry-Perot laser cavity containing methanol, pumped by a CO₂ laser. The frequencies are in the range 2.8 to 11.4 THz (105.4 to 26.2 µm). Ten of the measured frequencies are higher than 7 THz, and help to fill the laser frequency gaps in this region. Five of the measured lines are new. The 11.4 THz line has the highest frequency of an optically pumped laser ever measured with the CO₂ laser heterodyne technique.This work has been financed by the Brazilian Government - Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and by the United States Government - NASA Grant W-18, 623.Contribution of NIST, not subject to U.S. Copyright.     

Integrable non-linear σ models with fermions

The two-dimensional non-linear model on a Riemannian symmetric spaceM=G/H is coupled to fermions with quartic self-interactions. The resulting hybrid model is presented in a gauge-dependent formulation, with a bosonic field taking values inG and a fermionic field transforming under a given representation of the gauge groupH. General criteria for classical integrability are presented: they essentially fix the Lagrangian of the model but leave the fermion representation completely arbitrary. It is shown that by a special choice for the fermion representation (derived from the adjoint representation ofG by an appropriate reduction) one arrives naturally at the supersymmetric non-linear model onM=G/H. The issue of quantum integrability is also discussed, though with less stringent results.Work partially supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), Brazil, and KFA Jülich, Federal Republic of GermanyOn leave of absence from Fakultät für Physik der Universität Freiburg, Federal Republic of Germany     

The effects of concentration and temperature on the EFG generated by N.N. Pd impurities in a cubic Ag host

The time differential perturbed angular correlation (TDPAC) method is used to investigate the electric field gradients (EFG) generated by Pd impurity atoms alloyed into the cubic Ag host. As the concentration of the impurity is increased from 0.25 to 2.5 at.% we observed in detail how different near neighbour (n.n.) sites to the probe nuclei are populated, creating different EFG. The temperature dependence of the different EFG for a sample with 0.5 at.% of Pd showed that all follow theT ^3/2 law found previously for other doped cubic systems. In addition we observed that the n.n. population of impurities is strongly related to the thermal treatment of the sample.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico and Fianciadora de Estudos e Projectos.     

Observables in topological Yang-Mills theorieswith extended shift supersymmetry

We present a complete classification, at the classical level, of the observables of topological Yang-Mills theories with an extended shift supersymmetry of N generators, in any space-time dimension. The observables are defined as the Yang-Mills BRST cohomology classes of shift supersymmetry invariants. These cohomology classes turn out to be solutions of an N-extension of Witten's equivariant cohomology. This work generalizes results known in the case of shift supersymmetry with a single generator. Received: 8 March 2005, Published online: 21 October 2005 Supported in part by the Conselho Nacional de Desenvolvimento Científico e Tecnológico CNPq, Brazil     

Universal upper bound for the tunneling rate of a large quantum spin

An upper bound is derived for the tunneling rate of a spin with large spin quantum numberS. The bound isuniversal in the sense that it does not depend on the specific form of the anisotropy (i.e., the potential barrier). The method of proof relies on the exponential localization theorem of Fröhlich and Lieb and lends precise support to a rather suggestive interpretation put forth in a WKB analysis of van Hemmen and Süt. The resulting bound agrees with their expression for the tunneling rate in the limit of largeS.Supported in part by the Conselho Nacional de Desenvolvimento Cientifico e Technológico (CNPq)     

A new approximation for the dynamics of the transverse ising model

An improved mean field theory, the Reaction Field Approximation, which was previously used to obtain the static properties of model systems of localized spins (Heisenberg, XY, Ising and also more complicated interaction Hamiltonians) is extendend so that dynamical properties of the Ising model in presence of a transverse field can also be calculated. Theq- and -dependent susceptibility is obtained as function of field and temperature, from which the dynamic correlation functions can also be obtained. The dependence of the critical temperature on the transverse field is calculated and a phase diagram is presented.Work partly supported by Conselho Nacional de Desenvolvimento Cientifico e Tecnológico, CNPq, Brazil and by Alexander von Humboldt Stiftung, FRG     

Nuclear quadrupole interaction studies of high pressure phase transitions in InSb

Conclusions This study of the behavior of the EFG in the pressure-induced phase transition in InSb shows a high frequency in the high presure metallic phase, that is compatible with the tetragonal, -Sn like structure, but with a certain degree of imperfection. If this imperfection is in fact some disorder in the In and Sb positions, its amount could be promptly clarified by neutron diffraction, since the similarities of the atomic numbers of In and Sb preclude any easy measurement of superlattice lines by X-ray diffraction techniques.The strong frequency distribution that remains after the reversal of the phase transformation must be related with the peculiar kinetics of this reaction, since it depends on temperature and the time interval and since the same is not observed in the T1 transition. So it seems interesting to study other phase transitions in similar systems. A clarification of the precise nature of the generated defects demands the application of other techniques like transmission electron microsconv and neutron diffraction.If the defects observed here are in fact boundary of domains, it might be possible to relate the domain size with the frequency distribution and then to study, by TDPAC, the kinetics of formation and growth of these domains.Work supported in part by Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP)     

Extended feynman formula for forced harmonic oscillator

Horváthy's modification of Feynman's original method is generalized to the path integral formula of a forced harmonic oscillator. With this new formula the propagator of a harmonic oscillator with memory is evaluated exactly beyond and at caustics.Work supported in part by the Conselho Nacional de Desenvolvimento Cientifico e Tecnólogico (CNPq), Brazil.     

Electric field gradients created by near neighbour impurity atoms in a cubic silver host

The electric quadrupole interactions produced by near neighbour impurity atoms of Cu, Au, Zn, In, Sn and Bi on¹¹¹Cd probe nuclei in a cubic Ag lattice were studied by the TDPAC method. The effects of the type of impurity and its concentration have been investigated. The results show the presence of a high-frequency interactionv _Q ^h superimposed to a smeared out low frequencyv _Q ^l . The high frequency interaction, in the range 20 to 600 MHz, is attributed to impurity atoms located in nearest neighbour sites, while the low frequency interaction, in the range 2 to 12 MHz, is generated by impurities distributed at various different atomic distances from the probe nuclei. Bothv _Q ^h andv _Q ^l increase with impurity concentration leaving the ratiov _Q ^h /v _Q ^l almost constant. The results show that the high frequencyv _Q ^h is linearly dependent on the solute valence, and a logarithmic function of the impurity concentration, in the range 0.5 to 4.5 at. %. Large size effects have been observed in CuAg and BiAg alloys. Instead for ZnAg and SnAg, thev _Q ^h andv _Q ^l variation is attributed basically to charge effects.Work supported in part by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Financiadora de Estudos e Projetos (FINEP).     

A classicalN-body simulation of groups of galaxies

Summary Groups of galaxies are simulated by Monte Carlo technique. The mass distribution of the groups is assumed to follow a power law. Furthermore a linear relationship between mass and luminosity is considered. The calculated velocity dispersion is compared with the observational data and provides an estimate of the range in which the galaxy masses are distributed. It is shown, in this case, that the mass discrepancy can cover up two orders of magnitude, such as pointed out in the literature. The authors of this paper have agreed to not receive the proofs for correction. Supported by Conselho Nacional de Desenvolvimento Cientifico e Tecnológico, CNPq (Brasil).     

A global formalism for nonlinear waves in conservation laws

We introduce a unifying framework for treating all of the fundamental waves occurring in general systems ofn conservation laws. Fundamental waves are represented as pairs of states statisfying the Rankine-Hugoniot conditions; after trivial solutions have been eliminated by means of a blow-up procedure, these pairs form an (n+1)-dimensional manifold, the fundamental wave manifold. There is a distinguishedn-dimensional submanifold of containing a single one-dimensonal foliation that represents the rarefaction curves for all families. Similarly, there is a foliation of itself that represent shock curves. We identify othern-dimensional submanifolds of that are naturally interpreted as boundaries of regions of admissible shock waves. These submanifolds also have one-dimensional foliations, which represent curves of composite waves. This geometric framework promises to simplify greatly the study of the stability and bifurcation propertiesThis work was supported in part by: the NSF/CNP_q U.S.-Latin America Cooperative Science Program under Grant INT-8612605; the Institute for Mathematics and its Applications with funds provided by the National Science Foundation; the Air Force Office of Scientific Research under Grant AFOSR 90-0075; the National Science Foundation under Grant 8901884; the U.S. Department of Energy under Grant DE-FG02-90ER25084; the U.S. Army Research Office under Grant DAAL03-89-K-0017; the Financiadora de Estudos e Projetos; the Conselho Nacional de Desenvolvimento Científico e Tecnológica (CNP_q); the Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ); the Coordenação de Aperfeiçamento de Pessoal de Ensino Superior (CAPES); and the Sociedade Brasileira de Matemática (SBM)     

Q-spaces and the Foundations of Quantum Mechanics

Our aim in this paper is to take quite seriously Heinz Post’s claim that the non-individuality and the indiscernibility of quantum objects should be introduced right at the start, and not made a posteriori by introducing symmetry conditions. Using a different mathematical framework, namely, quasi-set theory, we avoid working within a label-tensor-product-vector-space-formalism, to use Redhead and Teller’s words, and get a more intuitive way of dealing with the formalism of quantum mechanics, although the underlying logic should be modified. We build a vector space with inner product, the Q-space, using the non-classical part of quasi-set theory, to deal with indistinguishable elements. Vectors in Q-space refer only to occupation numbers and permutation operators act as the identity operator on them, reflecting in the formalism the fact of unobservability of permutations. Thus, this paper can be regarded as a tentative to follow and enlarge Heinsenberg’s suggestion that new phenomena require the formation of a new “closed” (that is, axiomatic) theory, coping also with the physical theory’s underlying logic and mathematics. G. Domenech is a fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. D. Krause is a fellow of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil.     

On the Truncation of Systems with Non-Summable Interactions

In this note we consider long-range q-states Potts models on Z ^d , d≥ 2. For various families of non-summable ferromagnetic pair potentials φ(x)≥ 0, we show that there exists, for all inverse temperature β > 0, an integer N such that the truncated model, in which all interactions between spins at distance larger than N are suppressed, has at least q distinct infinite-volume Gibbs states. This holds, in particular, for all potentials whose asymptotic behaviour is of the type φ(x)∼ ‖x‖^−α, 0≤α≤ d. These results are obtained using simple percolation arguments. Work supported by Swiss National Foundation for Science, Conselho Nacional de Desenvolvimento Cientìfico e Tecnològico, and Programa de Auxìlio para Recèm Doutores PRPq-UFMG.     

The particle structure ofv-dimensional Ising models at low temperatures

In this work we study thev-dimensional Ising model at low temperatures and establish the existence of an upper gap in the energy-momentum spectrum of the two-point function forv3. Forv=2, it is known that this gap is absent.Supported in part by Conselho Nacional de Pesquisas (CNPq-Brazil), Universidade Federal de Minas Gerais (Brazil) and the National Science Foundation under Grant PHY76-17191