13,851 research outputs found
Opening the Pandora's box of quantum spinor fields
Lounesto's classification of spinors is a comprehensive and exhaustive
algorithm that, based on the bilinears covariants, discloses the possibility of
a large variety of spinors, comprising regular and singular spinors and their
unexpected applications in physics and including the cases of Dirac, Weyl, and
Majorana as very particular spinor fields. In this paper we pose the problem of
an analogous classification in the framework of second quantization. We first
discuss in general the nature of the problem. Then we start the analysis of two
basic bilinear covariants, the scalar and pseudoscalar, in the second quantized
setup, with expressions applicable to the quantum field theory extended to all
types of spinors. One can see that an ampler set of possibilities opens up with
respect to the classical case. A quantum reconstruction algorithm is also
proposed. The Feynman propagator is extended for spinors in all classes.Comment: 18 page
TWO-PION EXCHANGE NUCLEAR POTENTIAL - CHIRAL CANCELLATIONS
We show that chiral symmetry is responsible for large cancellations in the
two-pion exchange nucleon-nucleon interaction, which are similar to those
occuring in free pion-nucleon scattering.Comment: REVTEX style, 5 pages, 3 PostScrip figures compressed, tarred and
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NN Scattering: Chiral Predictions for Asymptotic Observables
We assume that the nuclear potential for distances larger than 2.5 fm is
given just by the exchanges of one and two pions and, for the latter, we adopt
a model based on chiral symmetry and subthreshold pion-nucleon amplitudes,
which contains no free parameters. The predictions produced by this model for
nucleon-nucleon observables are calculated and shown to agree well with both
experiment and those due to phenomenological potentials.Comment: 16 pages, 12 PS figures included, to appear in Physical Review
k-deformed Poincare algebras and quantum Clifford-Hopf algebras
The Minkowski spacetime quantum Clifford algebra structure associated with
the conformal group and the Clifford-Hopf alternative k-deformed quantum
Poincare algebra is investigated in the Atiyah-Bott-Shapiro mod 8 theorem
context. The resulting algebra is equivalent to the deformed anti-de Sitter
algebra U_q(so(3,2)), when the associated Clifford-Hopf algebra is taken into
account, together with the associated quantum Clifford algebra and a (not
braided) deformation of the periodicity Atiyah-Bott-Shapiro theorem.Comment: 10 pages, RevTeX, one Section and references added, improved content
Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon
Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10(17) m(-2). We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching. (C) 2015 Author(s).Dutch Polymer Institute (DPI), BISTABLE [704]; Fundacao para Ciencia e Tecnologia (FCT) through the research Instituto de Telecommunicacoes (IT-Lx); project Memristor based Adaptive Neuronal Networks (MemBrAiNN) [PTDC/CTM-NAN/122868/2010]; European Community Seventh Framework Programme FP7', ONE-P [212311]; Dutch Ministry of Education, Culture and Science (Gravity Program) [024.001.035]info:eu-repo/semantics/publishedVersio
Introduced population of ring-necked parakeets Psittacula krameri in Madeira Island, Portugal - call for an early action
Research ArticleAlien invasive species are major drivers of ecological change worldwide, being
especially detrimental in oceanic islands, where they constitute one of the greatest
threats to the survival of native species. Ring-necked parakeets Psittacula krameri
(Scopoli, 1769) are popular pets and individuals escaped from captivity have formed
multiple self-sustainable populations outside their native range. For over ten years,
free-ranging ring-necked parakeets have regularly been observed in Madeira Island
(Portugal) and strong evidence suggests that they have breed multiple times in
Funchal, the capital of the island. Herein, we assess the current status of Psittacula
krameri in Madeira and discuss the possible ecological and economic impacts of
established populations of this non-native parakeet. Given the initial stage of the
incursion, we advocate for a ârapid responseâ intervention aimed at preventing the
spread of this potential invaderinfo:eu-repo/semantics/publishedVersio
The quadratic spinor Lagrangian, axial torsion current, and generalizations
We show that the Einstein-Hilbert, the Einstein-Palatini, and the Holst
actions can be derived from the Quadratic Spinor Lagrangian (QSL), when the
three classes of Dirac spinor fields, under Lounesto spinor field
classification, are considered. To each one of these classes, there corresponds
a unique kind of action for a covariant gravity theory. In other words, it is
shown to exist a one-to-one correspondence between the three classes of
non-equivalent solutions of the Dirac equation, and Einstein-Hilbert,
Einstein-Palatini, and Holst actions. Furthermore, it arises naturally, from
Lounesto spinor field classification, that any other class of spinor field
(Weyl, Majorana, flagpole, or flag-dipole spinor fields) yields a trivial
(zero) QSL, up to a boundary term. To investigate this boundary term we do not
impose any constraint on the Dirac spinor field, and consequently we obtain new
terms in the boundary component of the QSL. In the particular case of a
teleparallel connection, an axial torsion 1-form current density is obtained.
New terms are also obtained in the corresponding Hamiltonian formalism. We then
discuss how these new terms could shed new light on more general
investigations.Comment: 9 pages, RevTeX, to be published in Int.J.Mod.Phys.D (2007
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