Field on Poincare Group and Quantum Description of Orientable Objects

We propose an approach to the quantum-mechanical description of relativistic orientable objects. It generalizes Wigner`s ideas concerning the treatment of nonrelativistic orientable objects (in particular, a nonrelativistic rotator) with the help of two reference frames (space-fixed and body-fixed). A technical realization of this generalization (for instance, in 3+1 dimensions) amounts to introducing wave functions that depend on elements of the Poincar, group G. A complete set of transformations that test the symmetries of an orientable object and of the embedding space belongs to the group I =GxG. All such transformations can be studied by considering a generalized regular representation of G in the space of scalar functions on the group, f(x,z), that depend on the Minkowski space points xaG/Spin(3,1) as well as on the orientation variables given by the elements z of a matrix ZaSpin(3,1). In particular, the field f(x,z) is a generating function of the usual spin-tensor multi-component fields. In the theory under consideration, there are four different types of spinors, and an orientable object is characterized by ten quantum numbers. We study the corresponding relativistic wave equations and their symmetry properties.

Light-front model of the kaon electromagnetic current

The kaon electromagnetic form factor is extracted from both components of the current: J(+) and J(-) with a pseudo-scalar coupling of the quarks to the meson. The pair production process does not contribute to J(+) in the Drell-Yan frame (q(+) = 0). However, the pair production process contribution is different from zero in J(-) and this contribution is necessary to keep the rotational symmetry properties of the current.

Localized modes of binary mixtures of Bose-Einstein condensates in nonlinear optical lattices

The properties of the localized states of a two-component Bose-Einstein condensate confined in a nonlinear periodic potential (nonlinear optical lattice) are investigated. We discuss the existence of different types of solitons and study their stability by means of analytical and numerical approaches. The symmetry properties of the localized states with respect to nonlinear optical lattices are also investigated. We show that nonlinear optical lattices allow the existence of bright soliton modes with equal symmetry in both components and bright localized modes of mixed symmetry type, as well as dark-bright bound states and bright modes on periodic backgrounds. In spite of the quasi-one-dimensional nature of the problem, the fundamental symmetric localized modes undergo a delocalizing transition when the strength of the nonlinear optical lattice is varied. This transition is associated with the existence of an unstable solution, which exhibits a shrinking (decaying) behavior for slightly overcritical (undercritical) variations in the number of atoms.

Medidas de ressonância de spin eletrônico (RSE) em polianilina dopada com plastificante e de condutividade a.c. e RSE em óxidos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Measurement of the rotational inertia of bodies by using mechanical spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Theoretical study of correlated systems using hybrid functionals

Diese Arbeit unterstreicht das Potential von Hybridfunktionalen (B3LYP) für die Untersuchung einer großen Bandbreite von Systemen. Durch die Einbeziehung der exakten Hartree-Fock Austauschenergie kann B3LYP für molekulare und kristalline Systeme eingesetzt werden. Zum Beispiel können stark korrelierte Systeme mit B3LYP erfolgreich erforscht werden. Die elektronische Struktur von PAHs wurde mit B3LYP Hybriddichtefunktionalen untersucht. Mit der ∆SCF-Methode wurden Elektronenbindungsenergien bestimmt, welche die mit UPS gewonnenen experimentellen Resultate bestätigen und ergänzen. Symmetrieeigenschaften der molekularen Orbitale wurden analysiert, um eine Zuordnung und Einschätzung der zugehörigen Signalstärke zu ermöglichen. Während σ-artige Orbitale nur schwer durch UPS-Messungen an dünnen Filmen detektiert werden können, bieten Rechnungen eine detaillierte Einsicht in die verborgenen Teile der Spektren.rnWeiterhin wurden π−π-Komplexe untersucht, welche von verschiedenen Donor- und Akzeptor-Molekülen gebildet werden. Die Moleküle basieren auf polyzyklischen, aromatischen Kohlenwasserstoffen. Für Ladungstransferkomplexe finden DFT Rechnungen ein Minimum in der Oberfläche der potentiellen Energie. Diese attraktive Wechselwirkung wird durch Coulombanziehung verursacht. Allerdings ist die Coulombanziehung nicht die stärkste Wechselwirkung in Ladungstransferkomplexen. Die Einbeziehung von van der Waals-Korrekturen verbessert den intermolekularen Abstand und die Bindungsenergie.rnEine Verkleinerung der intermolekularen Abstände führt zu einer großen Verschiebung der HOMO- und LUMO-Energie.rnAus der Klasse der kristallinen korrelierten Systeme wurden Rb4O6 und FeSe untersucht. Im Falle von Rb4O6 führen Ladungsordnung und Korrelationen zu einem isolierenden Grundzustand. Das hypothetische druckabhängige Phasendiagramm wurde untersucht. Eine Erhöhung des Drucks führt zu einer vergrößerten Bandlücke. Bei etwa 75 GPa wird die Bandbreite W größer als der Bandabstand U und das System nimmt einen homogen gemischt valenten Zustand mit teilweise besetzten π−π-Orbitalen an. Für Drücke ab 160 GPa wird W sehr viel größer als U und das System wird metallisch.rnIm Fall von FeSe finden wir eine korrelierte und isolierende Phase bei hohen Drücken, während das System bei niedrigen Drücken supraleitendes Verhalten zeigt. Die Berechnungen der Elektronenstruktur mit dem Hybridfunktional B3LYP führt zum korrekten halbleitenden Grundzustand in der NiAs- und MnP-Struktur von FeSe. Die Rolle der Korrelationen, der Stöchiometrie und der Nähe zum Magnetismus wird besprochen. Im Speziellen wird gezeigt, dass die Phase mit NiAs-Struktur starke lokale Korrelationen aufweist, was zu einem halbleitenden Zustand in einem weiten Druckbereich führt.

Self-dual continuous processes

The important application of semi-static hedging in financial markets naturally leads to the notion of conditionally quasi self-dual processes which is, for continuous semimartingales, related to conditional symmetry properties of both their ordinary as well as their stochastic logarithms. We provide a structure result for continuous conditionally quasi self-dual processes. Our main result is to give a characterization of continuous Ocone martingales via a strong version of self-duality.

Multiasset Derivatives and Joint Distributions of Asset Prices

Several of multiasset derivatives like basket options or options on the weighted maximum of assets exhibit the property that their prices determine uniquely the underlying asset distribution. Related to that the question how to retrieve this distributions from the corresponding derivatives quotes will be discussed. On the contrary, the prices of exchange options do not uniquely determine the underlying distributions of asset prices and the extent of this non-uniqueness can be characterised. The discussion is related to a geometric interpretation of multiasset derivatives as support functions of convex sets. Following this, various symmetry properties for basket, maximum and exchange options are discussed alongside with their geometric interpretations and some decomposition results for more general payoff functions.

Symmetries in geology and geophysics

Symmetries have played an important role in a variety of problems in geology and geophysics. A large fraction of studies in mineralogy are devoted to the symmetry properties of crystals. In this paper, however, the emphasis will be on scale-invariant (fractal) symmetries. The earth’s topography is an example of both statistically self-similar and self-affine fractals. Landforms are also associated with drainage networks, which are statistical fractal trees. A universal feature of drainage networks and other growth networks is side branching. Deterministic space-filling networks with side-branching symmetries are illustrated. It is shown that naturally occurring drainage networks have symmetries similar to diffusion-limited aggregation clusters.

CP properties of symmetry-constrained two-Higgs-doublet models

The two-Higgs-doublet model can be constrained by imposing Higgs-family symmetries and/or generalized CP symmetries. It is known that there are only six independent classes of such symmetry-constrained models. We study the CP properties of all cases in the bilinear formalism. An exact symmetry implies CP conservation. We show that soft breaking of the symmetry can lead to spontaneous CP violation (CPV) in three of the classes.

Dynamical (super)symmetry vacuum properties of the supersymmetric Chern-Simons-matter model

By computing the two-loop effective potential of the D=3 N=1 supersymmetric Chern-Simons model minimally coupled to a massless self-interacting matter superfield, it is shown that supersymmetry is preserved, while the internal U(1) and the scale symmetries are broken at two-loop order, dynamically generating masses both for the gauge superfield and for the real component of the matter superfield.

Broken symmetry and critical transport properties of random metals

Recent experimental data on the conductivity σ+(T), T → 0, on the metallic side of the metal–insulator transition in ideally random (neutron transmutation-doped) 70Ge:Ga have shown that σ+(0) ∝ (N − Nc)μ with μ = ½, confirming earlier ultra-low-temperature results for Si:P. This value is inconsistent with theoretical predictions based on diffusive classical scaling models, but it can be understood by a quantum-directed percolative filamentary amplitude model in which electronic basis states exist which have a well-defined momentum parallel but not normal to the applied electric field. The model, which is based on a new kind of broken symmetry, also explains the anomalous sign reversal of the derivative of the temperature dependence in the critical regime.

Electronic properties and hyperfine fields of nickel-related complexes in diamond

We carried out a first-principles investigation on the microscopic properties of nickel-related defect centers in diamond. Several configurations, involving substitutional and interstitial nickel impurities, have been considered either in isolated configurations or forming complexes with other defects, such as vacancies and boron and nitrogen dopants. The results, in terms of spin, symmetry, and hyperfine fields, were compared with the available experimental data on electrically active centers in synthetic diamond. Several microscopic models, previously proposed to explain those data, have been confirmed by this investigation, while some models could be discarded. We also provided insights into the microscopic structure of several of those centers.

Critical Properties at the Field-Induced Bose-Einstein Condensation in NiCl(2)-4SC(NH(2))(2)

We report new magnetization measurements on the spin-gap compound NiCl(2)-4SC(NH(2))(2) at the low-field boundary of the magnetic field-induced ordering. The critical density of the magnetization is analyzed in terms of a Bose-Einstein condensation of bosonic quasiparticles. The analysis of the magnetization at the transition leads to the conclusion for the preservation of the U(1) symmetry, as required for Bose-Einstein condensation. The experimental data are well described by quantum Monte Carlo simulations.