Electromagnetic structure and weak decay of meson K in a light-front QCD-inspired model

The kaon electromagnetic (e.m.) form factor is reviewed considering a light-front constituent quark model. In this approach, it is discussed the relevance of the quark-antiquark pair terms for the full covariance of the e.m. current. It is also verified, by considering a QCD dynamical model, that a good agreement with experimental data can be obtained for the kaon weak decay constant once a probability of about 80% of the valence component is taken into account.

Pion structure in the instanton liquid model

The covariant quark model of the pion based on the effective nonlocal quark-hadron Lagrangian involving nonlocality induced by instanton fluctuations of the QCD vacuum is reviewed. Explicit gauge invariant formalism allows us to construct the conserved vector and axial currents and to demonstrate their consistency with the Ward-Takahashi identities and low-energy theorems. The spontaneous breaking of chiral symmetry results in the dynamic quark mass and the vertex of the quark-pion interaction, both momentum-dependent. The parameters of the instanton vacuum, the average size of the instantons, and the effective quark mass are expressed in terms of the vacuum expectation values of the lowest dimension quark-gluon operators and low-energy pion observables. The transition pion form factor for the processes gamma*gamma --> pi (0) and gamma*gamma* --> pi (0) is analyzed in detail. The kinematic dependence of the transition form factor at high momentum transfers allows one to determine the relationship between the light-cone amplitude of the quark distribution in the pion and the quark-pion vertex function. Its dynamic dependence implies that the transition form factor gamma*gamma --> pi (0) at high momentum transfers is acutely sensitive to the size of the nonlocality of nonperturbative fluctuations in the QCD vacuum. In the leading twist, the distribution amplitude and the distribution function of the valence quarks in the pion are calculated at a low normalization point of the order of the inverse average instanton size rho (-1)(c). The QCD results are evolved to higher momentum transfers and are in reasonable agreement with available experimental data on the pion structure.

Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model

We study the scaling of the S-3(1)-S-1(0) meson mass splitting and the pseudoscalar weak-decay constants with the mass of the meson, as seen in the available experimental data. We use an effective light-front QCD-inspired dynamical model regulated at short distances to describe the valence component of the pseudoscalar mesons. The experimentally known values of the mass splitting, decay constants (from global lattice-QCD averages) and the pion charge form factor up to 4 [GeV/c](2) are reasonably described by the model.

The effect of core electrons in e(+)-Na scattering

The scattering of positrons off sodium targets has been investigated using the coupled static model. The sodium atom is represented by the one-active-electron model in which all the electrons of the target have been considered explicitly and the loosely bound valence electron is only involved in transitions. The scattering parameters are presented at low and medium energies. Appreciable differences are noticed between the present results and those obtained by the one-electron model with and without the core potential.

The small x behavior of the gluon strucutre function from total cross-sections

Within a QCD-based eikonal model with a dynamical infrared gluon mass scale we discuss how the small x behavior of the gluon distribution function at moderate Q(2) is directly related to the rise of total hadronic cross-sections. In this model the rise of total cross-sections is driven by gluon-gluon semihard scattering processes, where the behavior of the small x gluon distribtuion function exhibits the power law xg(x, Q(2)) = h(Q(2))x(-epsilon). Assuming that the Q(2) scale is proportional to the dynamical gluon mass one, we show that the values of h(Q(2)) obtained in this model are compatible with an earlier result based on a specific nonperturbative Pomeron model. We discuss the implications of this picture for the behavior of input valence-like gluon distributions at low resolution scales.

Cosmological forecasts from photometric measurements of the angular correlation function

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Triangular-lattice anisotropic dimerized Heisenberg antiferromagnet: Stability and excitations of the quantum paramagnetic phase

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

Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Understanding the origin of photoluminescence in disordered Ca0.60Sr0.40WO4: An experimental and first-principles study

Visible photoluminescence (PL) was observed for the first time at room temperature in structurally disordered calcium strontium tungstate powder, Ca0.60Sr0.40WO4 (CSW), obtained by the polymeric precursor method. The PL behavior of CSW powders has been analyzed as a function of the disorder rate, based on experimental and theoretical studies. Quantum mechanical theory based on density functional theory at the B3LYP level has been employed to study the electronic structure of two periodic models representing both crystalline and disordered powders. Their electronic structures have been analyzed in terms of density of states, band dispersion and charge densities. The calculations indicate a break in symmetry when passing from crystalline to disordered models, creating localized electronic levels above the valence band. Moreover, a negative charge transfer process takes place from the [WO3] cluster to the [WO4] cluster. The polarization induced by the break in symmetry and the existence of localized levels favors the creation of trapped holes and electrons, originating the PL phenomenon. (c) 2007 Elsevier B.V. All rights reserved.

Piezoresponse behavior of niobium doped bismuth ferrite thin films grown by chemical method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Coloring ionic trapping states in WO3 and Nb2O5 electrochromic materials

Complex electro-optical analysis is a very useful approach to separate different kinetic processes that occur during ionic insertion reactions in electrochromic oxide materials. In this paper, we use this type of combined technique to investigate ionic and optical changes in different oxide host systems, i.e., in two oxide hosts, specifically WO3 and Nb2O5. A comparison of their electro-optical responses revealed the presence of an ionic trapping contribution to the kinetics of the coloring sites, which was named here as coloring ionic trapping state. As expected, this coloring trapping process is slower in Nb2O5 since the reduction potential of Nb2O5 is more negative (more energy is needed for a higher degree of coloration). A phenomenological solid-state model that encompasses homogeneous charge transfer and valence trapping was proposed to explain the coloring ionic trapping process. Basically the model is able to explain how ionic dynamics at low frequency region, i.e., the slower kinetic step, controls the coloring kinetics, i.e., how it is capable to regulate the coloring rates.Optical transient analyses demonstrated the possibility of the presence of more than one coloring ionic trap, indicating the complexity of the processes involved in coloration phenomenon in metal oxide host systems. (C) 2008 Published by Elsevier Ltd.

Shell utilization pattern of the hermit crab Clibanarius vittatus (Crustacea, Anomura) in an estuary at São Vicente, State of São Paulo, Brazil

O objetivo do presente estudo foi avaliar a utilização de conchas de gastrópodes por Clibanarius vittatus (Bosc, 1802), na Praia dos Pescadores, em São Vicente (SP), Brasil. Foram realizadas amostras mensais no período de maio de 2001 a abril de 2003, na região intertidal durante a maré baixa. Todos os animais foram pesados e tiveram o comprimento de seu escudo cefalotorácico mensurados, suas conchas identificadas e medidas quanto ao comprimento (mm), abertura (mm) e peso (g). Capturamos 2.344 ermitões (644 machos, 1.594 fêmeas não-ovígeras, 45 fêmeas ovígeras e 61 em intersexo), utilizando 13 espécies de conchas de gastrópodes, das quais Stramonita haemastoma (Linnaeus, 1767), Cymatium parthenopeum (Von Salis, 1793) e Achatina fulica (Bowdich, 1822) representaram mais de 98% das conchas utilizadas. Obteve-se significativa diferença de tamanho entre os sexos, com machos e indivíduos em intersexo atingindo maior porte físico do que fêmeas. Este padrão influenciou fortemente na ocupação e utilização de conchas, principalmente em A. fulica, que foi a maior concha obtida por C. vittatus, utilizada somente por machos e indivíduos em intersexo. Cymatium parthenopeum foi a única espécie de concha em que se obtiveram elevados coeficientes de determinação para todas os parâmetros analisados. Stramonita haemastoma apresentou elevados e significativos coeficientes de determinação, indicando que esta espécie é o principal recurso de concha ocupada na Praia dos Pescadores.

On a record of Dardanus venosus (H. Milne Edwards) (Crustacea, Anomura) from the São Paulo State, Brazil

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

Enriquecimento da dieta do bicho-da-seda com extrato hidrossolúvel de soja

O objetivo deste trabalho foi avaliar se a suplementação da dieta do bicho-da-seda com extrato hidrossolúvel de soja (EHS) interfere na produção de casulos e no consumo de folhas de amoreira (Morus alba L.) de diferentes cultivares pelas lagartas. O delineamento experimental utilizado foi o inteiramente casualizado em esquema fatorial 4x5, com quatro cultivares de amoreira ('IZ64', 'IZ56/4', 'FM86' e 'FMSM') e cinco dietas (folhas não tratadas, folhas umedecidas com água, folhas enriquecidas com EHS, em três níveis: suplementação da dieta com 5, 10 e 20% de PB). O EHS foi aspergido sobre as folhas, tendo a água como agente dispersante. O consumo foi verificado pela diferença entre a quantidade de folhas fornecidas e a quantidade não consumida pelas lagartas. A ingestão de alimento apresentou-se de forma quadrática, diminuindo à medida que o EHS foi adicionado à dieta. Houve interação dos fatores cultivar e dieta. O fornecimento de folhas de amoreira com acréscimo proteico de 10% por meio do EHS melhorou a qualidade dos casulos do bicho-da-seda com a utilização das cultivares 'IZ56/4' e 'FMSM'. A pulverização de EHS nas folhas da cultivar 'IZ64' prejudicou a produção de casulos. Lagartas do bicho-da-seda, alimentadas com folhas de amoreira sem suplementação, produziram cascas séricas mais pesadas com folhas das cultivares 'IZ64' e 'FMSM'. A aspersão de água nas folhas incrementou o peso de cascas séricas produzidas a partir da cultivar 'FM86'. A suplementação da dieta com EHS diminui o consumo da lagarta do bicho-da-seda. A aplicação de EHS influencia a produção de casulos em função da cultivar utilizada.

Spin-1 particle in the light-front approach

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