Nonforward parton distributions of the pion within an effective single instanton approximation

We develop a relativistic quark model for pion structure, which incorporates the nontrivial structure of the vacuum of quantum chromodynamics as modelled by instantons. Pions are bound states of quarks and the strong quark-pion vertex is determined from an instanton induced effective Lagrangian. The interaction of the constituents of the pion with the external electromagnetic field is introduced in gauge invariant form. The parameters of the model, i.e., effective instanton radius and constituent quark mass, are obtained from the vacuum expectation values of the lowest dimensional quark and gluon operators and the low-energy observables of the pion. We apply the formalism to the calculation of the pion form factor by means of the isovector nonforward parton distributions and find agreement with the experimental data. © 2000 Elsevier Science B.V.

Pion structure function within the instanton model

The leading-twist valence-quark distribution function in the pion is obtained at a low normalization scale of an order of the inverse average size of an instanton pc. The momentum dependent quark mass and the quark-pion vertex are constructed in the framework of the instanton liquid model, using a gauge invariant approach. The parameters of instanton vacuum, the effective instanton radius and quark mass, are related to the vacuum expectation values of the lowest dimension quark-gluon operators and to the pion low energy observables. An analytic expression for the quark distribution function in the pion for a general vertex function is derived. The results are QCD evolved to higher momentum-transfer values, and reasonable agreement with phenomenological analyses of the data on parton distributions for the pion is found. ©2000 The American Physical Society.

Pion-distribution amplitude within the instanton model

The leading-twist pion-distribution amplitude is obtained at a low normalization scale of order ρc (inverse average size of an instanton). Pion dynamics, consistent with gauge invariance and low-energy theorems, is considered within the instanton vacuum model. The results are QCD-evolved to higher momentum-transfer values and are in agreement with recent data from CLEO on the pion transition form factor. It is also shown that some previous calculations violate the axial Ward-Takahashi identity. © 2001 MAIK Nauka/Interperiodica.

First measurement of π-e→π-eγ pion virtual compton scattering

Pion virtual compton scattering (VCS) via the reaction π-e→π-eγ was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c π- beam incident on target atomic electrons, detecting the incident π- and the final state π-, electron and γ. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding π- VCS experimental cross section is σ=38.8±13 nb, in agreement with the theoretical expectation of σ=34.7 nb.

Electromagnetic form factor of the pion in the space- and time-like regions within the front-form dynamics

The pion electromagnetic form factor is calculated in the space- and time-like regions from -10 (GeV/c)2 up to 10 (GeV/c)2, within a front-form model. The dressed photon vertex where a photon decays in a quark-antiquark pair is depicted generalizing the vector meson dominance ansatz, by means of the vector meson vertex functions. An important feature of our model is the description of the on-mass-shell vertex functions in the valence sector, for the pion and the vector mesons, through the front-form wave functions obtained within a realistic quark model. The theoretical results show an excellent agreement with the data in the space-like region, while in the time-like region the description is quite encouraging. © 2003 Elsevier B.V. All rights reserved.

Time-like and space-like pion form factors within front-form dynamics

An approach for a unified description of the pion electromagnetic form factor in the space- and time-like regions, within a constituent quark model on the light front is briefly illustrated. Three main ingredients enter our approach: i) the on-shell quark-hadron vertex functions in the valence sector, ii) the dressed photon vertex where a photon decays in a quark-antiquark pair, and iii) the emission and absorption amplitudes of a pion by a quark. © 2005 American Institute of Physics.

Anomalia congênita em vasos da base do coração de um potro

Congenital anomalies of heart and large vessels are among more common found in animals, however rare in horses. This survey describes a cardiac anomaly that presents confluence between aorta wall and lung trunk, ramification of caudal cava vein in left atrium with presence of valve and consequently erroneous position of heart in thoracic cavity of one foal found dead after birth. The diagnostic was carried out for macroscopic finds association during the necropsy and histopathologic exams carried out at School of Veterinary Medicine - Unesp Araçatuba.

Proteção miocárdica ao coração hipertrofiado: O eterno desafio

The myocardial protection allowed great advance in cardiac surgery, decreasing the mortality and making more feasible complex surgeries. Latterly, the patient population elected for cardiac procedures has been changing towards elderly patients with ventricular function depressed and myocardial hypertrophy. The myocardial hypertrophy condition represents a great challenge since the beginning of the cardiac surgery. Several techniques have been described to protect the myocardial hypertrophy, however with no satisfactory results. In this manuscript we present the state of the art technique of myocardial protection.

A Combined Study of the Pion's Static Properties and form Factors

We study consistently the pion's static observables and the elastic and γ* γ → π0 transition form factors within a light-front model. Consistency requires that all calculations are performed within a given model with the same and single adjusted length or mass-scale parameter of the associated pion bound-state wave function. Our results agree well with all extent data including recent Belle data on the γ* γ → π0 form factor at large q2, yet the BaBar data on this transition form factor resists a sensible comparison. We relax the initial constraint on the bound-state wave function and show the BaBar data can partially be accommodated. This, however, comes at the cost of a hard elastic form factor not in agreement with experiment. Moreover, the pion charge radius is about 40 % smaller than its experimentally determined value. It is argued that a decreasing charge radius produces an ever harder form factor with a bound-state amplitude difficultly reconcilable with soft QCD. We also discuss why vector dominance type models for the photon-quark vertex, based on analyticity and crossing symmetry, are unlikely to reproduce the litigious transition form factor data. © 2013 Springer-Verlag Wien.

A formação da historiografia teatral brasileira (1888-1938): consonâncias e dissonâncias

Pós-graduação em Artes - IA

O português brasileiro cantado: normas de 1938 e 2007, análise compárativa para interpretação de obras vocais em idioma brasileiro

Pós-graduação em Música - IA

Influência do diabetes mellitus no coração de ratos senescentes espontaneamente hipertensos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

As experiências femininas na AIB, 1932-1938: revendo o passado : gênero e representações

Pós-graduação em Ciências Sociais - FFC

Avaliação morfofisiológica do coração de atletas de diferentes modalidades esportivas

Pós-graduação em Pesquisa e Desenvolvimento (Biotecnologia Médica) - FMB

Influência da deficiência de taurina no coração

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)