Relativistic dynamics of Qqq systems

The bound state of constituent quarks forming a $Qqq$ composite baryon is investigated in a QCD-inspired effective light-front model. The light-front Faddeev equations are derived and solved numerically. The masses of the spin 1/2 low-lying states of the nucleon, $\Lambda^0$, $\Lambda^+_c$ and $\Lambda^0_b$ are found and compared to the experimental data. The data is qualitatively described with a flavor independent effective interaction.Comment: 18 pages, include 6 figures, 2 eps figures, use latex, revtex. To appear Phys. Rev D (2002

Ground State Masses and Biding Energies of the Nucleon, Hyperon and Heavy Baryons in a Light-Front Model

The ground state masses and binding energies of the nucleon, $\Lambda^0$, $\Lambda^+_c$, $\Lambda^0_b$ are studied within a constituent quark QCD-inspired light-front model. The light-front Faddeev equations for the $Qqq$ composite spin 1/2 baryons, are derived and solved numerically. The experimental data for the masses are qualitatively described by a flavor independent effective interaction.Comment: 13 pages, include 4 eps figures, use latex, revte

Relativistic Quark Spin Coupling Effects in the Nucleon Electromagnetic Form Factors

We investigate the effect of different forms of relativistic spin coupling of constituent quarks in the nucleon electromagnetic form factors. The four-dimensional integrations in the two-loop Feynman diagram are reduced to the null-plane, such that the light-front wave function is introduced in the computation of the form factors. The neutron charge form factor is very sensitive to different choices of spin coupling schemes, once its magnetic moment is fitted to the experimental value. The scalar coupling between two quarks is preferred by the neutron data, when a reasonable fit of the proton magnetic momentum is found.Comment: 13 pages, needs axodraw.ps and axodraw.sty for diagrams of Fig.

Investigações sobre as possibilidades de operação de suposição de sujeito na situação de internação do recém-nascido pré-termo em UTI neonatal

La prématurité et l'hospitalisation du bébé dans l'unité de soins intensifs néonatals comportent une situation potentiellement traumatisante, capable d'affaiblir la fonction maternelle et d'établir le lien affectif mère-bébé, fondamental pour la constitution subjective de l'enfant. Cette recherche a examiné la constitution subjective du bébé prématurément hospitalisé à partir de la référence psychanalytique théorique et clinique et de l'application du premier groupe d'âge (0 à 4 mois incomplets) du protocole IRDI - indicateurs cliniques de risque pour le développement de l'enfant. L'enquête s'est concentrée sur les possibilités d'opération de prise en charge du sujet dans la situation d'hospitalisation du nouveau-né prématuré. Il a été vérifié qu'il était possible pour l'agent de la fonction maternelle de produire l'anticipation du sujet chez l'enfant, même dans la situation atypique de l'hospitalisation du bébé.A prematuridade e internação do bebê em Unidade de Terapia Intensiva Neonatal compreendem situação potencialmente traumática, capaz de fragilizar o exercício da função materna e estabelecimento do laço afetivo mãe-bebê, fundamentais para a constituição subjetiva da criança. Esta pesquisa investigou a constituição subjetiva do bebê prematuro hospitalizado a partir do referencial teórico-clínico psicanalítico e aplicação da primeira faixa etária (0 a 4 meses incompletos) do protocolo IRDI – Indicadores Clínicos de Risco para o Desenvolvimento Infantil. Tomou-se como foco de investigação as possibilidades de operação de suposição de sujeito na situação de hospitalização do recém-nascido pré-termo. Verificou-se que foi possível para o agente da função materna produzir a antecipação de sujeito no filho, mesmo na situação atípica de internação do bebê.La prematuridad y la hospitalización del bebé en la Unidad de Cuidados Intensivos Neonatales incluyen una situación potencialmente traumática, capaz de debilitar la función materna y establecer el vínculo afectivo madre-bebé, fundamental para la constitución subjetiva del niño. Se investigó la constitución subjetiva del bebé prematuramente hospitalizado a partir de la referencia teórico-clínica psicoanalítica y la aplicación del primer grupo de edad (0 a 4 meses incompletos) del protocolo IRDI - Indicadores Clínicos de Riesgo para el Desarrollo Infantil. La investigación se centró en las posibilidades de operación de asunción del sujeto en la situación de hospitalización del recién nacido prematuro. Se comprobó que era posible que el agente de la función materna produjera la anticipación del sujeto en el niño, incluso en la situación atípica de hospitalización del bebé.Prematurity and hospitalization of the baby in the Neonatal Intensive Care Unit include a potentially traumatic situation, capable of weakening the maternal function and establishing the mother-baby affective bond, which is fundamental for the child's subjective constitution. This research investigated the subjective constitution of the prematurely hospitalized baby from the psychoanalytical theoretical-clinical reference and application of the first age group (0 to 4 incomplete months) of the IRDI protocol – Clinical Indicators of Risk for Child Development. The focus of the investigation was on the possibilities of subject assumption operation in the preterm newborn's hospitalization situation. It was verified that it was possible for the maternal function agent to produce the anticipation of the subject in the child, even in the atypical situation of hospitalization of the baby

Light-Front Model of Transition Form-Factors in Heavy Meson Decay

Electroweak transition form factors of heavy meson decays are important ingredients in the extraction of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements from experimental data. In this work, within a light-front framework, we calculate electroweak transition form factor for the semileptonic decay of $D$ mesons into a pion or a kaon. The model results underestimate in both cases the new data of CLEO for the larger momentum transfers accessible in the experiment. We discuss possible reasons for that in order to improve the model.Comment: Paper with 5 pages and 2 eps figures. To appear to Nuclear Physics B. Talk at Light Cone 2009: Relativistic Hadronic and Particle Physics (LC 2009), Sao Jose dos Campos, S.P, Brazil, 8-13 Jul 2009

Three-Fermion Bound States on the Light Front

We investigate the stability of the relativistic three-fermion system with a zero-range force in the light front form. In particular, introducing an invariant cut-off, we study the dependence of the bound state on the coupling strength also for cases where the two-fermion system is unbound. The relativistic Thomas collapse is discussed by solving the fully coupled integral equation system. Furthermore, we explicitly investigate the ground state mass of the three-fermion system and compare to previous simplified calculations.Comment: 23 pages, 6 figure

Relativistic Quark Spin Coupling Effects in the Correlations Between Nucleon Electroweak Properties

We investigate the effect of different relativistic spin couplings of constituent quarks on nucleon electroweak properties. Within each quark spin coupling scheme the correlations between static electroweak observables are found to be independent of the particular shape of the momentum part of the nucleon light-front wave function. The neutron charge form factor is very sensitive to different choices of spin coupling schemes once the magnetic moment is fitted to the experimental value. However, it is found rather insensitive to the details of the momentum part of the three-quark wave function model.Comment: 23 pages, 13 figures, requires axodraw.sty 1 figure corrected, 1 refs. added, some changes in tex

Projecting the Bethe-Salpeter Equation onto the Light-Front and back: A Short Review

The technique of projecting the four-dimensional two-body Bethe-Salpeter equation onto the three-dimensional Light-Front hypersurface, combined with the quasi-potential approach, is briefly illustrated, by placing a particular emphasis on the relation between the projection method and the effective dynamics of the valence component of the Light-Front wave function. Some details on how to construct the Fock expansion of both i) the Light-Front effective interaction and ii) the electromagnetic current operator, satisfying the proper Ward-Takahashi identity, will be presented, addressing the relevance of the Fock content in the operators living onto the Light-Front hypersurface. Finally, the generalization of the formalism to the three-particle case will be outlined.Comment: 16 pages, macros included. Mini-review to be printed in a regular issue of Few-Body Systems devoted to the Workshop on "Relativistic Description of Two- and Three-body Systems in Nuclear Physics" ECT* Trento, 19 - 23 October 200

Q2Q^2 Independence of QF2/F1QF_2/F_1, Poincare Invariance and the Non-Conservation of Helicity

A relativistic constituent quark model is found to reproduce the recent data regarding the ratio of proton form factors, $F_2(Q^2)/F_1(Q^2)$. We show that imposing Poincare invariance leads to substantial violation of the helicity conservation rule, as well as an analytic result that the ratio $F_2(Q^2)/F_1(Q^2)\sim 1/Q$ for intermediate values of $Q^2$.Comment: 13 pages, 7 figures, to be submitted to Phys. Rev. C typos corrected, references added, 1 new figure to show very high Q^2 behavio