REINA() DE TRABALHO SOBRE FiSICA NUCLEAR NO BRASIL

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$Electronic Structure of Substitutional 3D Impurities in $\gamma$

XX RTFINIR Resumos distances. [1] G. Brown and D. W. Durso, Phys. Lett. 1335 (1971) 120 CHIRAL SYMMETRY AND NUCLEON-NUCLEON SCATTERING MANUEL ROBERT() ROBILOTTA Institute de Fisica, Universidade de Silo Paula JOEL CdSAR PEPIN Institute de Fisica 'Tedrica, Universidade Estadual Paulista We assume that the nucleon-nucleon interaction for low and intermediate energies is given just by the exchanges of one and two pions. In the latter case we adopt a model based on chiral symmetry and subthreshold pionnucleon interaction amplitude, which contains no free parameters. Chiral symmetry is very relevant because it is the responsible for the organization of various processes into autonomous families. This gives rise to cancellations in the intermediate pion-nucleon interaction, which is the main building block of the nucleon-nucleon interaction. The subthreshold pion-nucleon amplitude is supplemented by empirical information in the form of the Miler, Jacob and Strauss (HIS) coefficients. Predictions from this model for nucleon-nucleon observables are calculated in the momentum space and compared with experimental data. Null Plane Model of Proton W. R. B. DE ARAXT.10, J. P. 13. C. DE MELD Thstituto de Fisica, Universidade de Siio Paulo T. FREDERIC° Depto. de Fisica, ITA, Centro Tdcnieo Acrocspacial, Sao Jose dos Campos, Siin Paulo We present a calculation of the proton electric formfactor (GB(9 2)), using a three quark Faddeev wavefunction in the null-plane[1]. The null-plane wavefunction is obtained from the solution of the Faddeev equation with zero-range force acting between the constituent quarks. No confinement is present in our effective model. The totally symmetric spatial part of the wave-function is obtained numerically in a threeboson calculation. We use the covariance of the proton model under kinematical front-form boosts to calculate GE(q 2), and compare our numerical results with the available experimental data. GE(q 2) scales with q4 in the asymptotic region and describes the data for low momentum transfers. Our attempt, using such a schematical model, is based on the notion of relativistic constituent quarks. We have also seen examples in the literature [2], in which the spontaneous breaking of chiral symmetry creates the constituent quark mass. Such a mechanism is modeled using the Nambu-Jona-Lasinio contact interaction and applied to hadronic phenomenology. Our schematical model has both ingredients together: relativistic constituent quark and a contact interaction. We test the totally symmetric spatial part of the proton wave-function with these two minimal ingredients in a calculation of the proton eletric form-factor. The confinement has no explicit role in the model but is buried in the effective degrees of freedom. Relativistic dynamics is required by the mass of the constituent quarks and the size of the nucleon wave-function. The reason for choosing a three boson dynamics, is to just concentrate on the specific form of the spatial wave-function, and obtain insight in to it without the complications arising with the use of the spin. The relativistic spin structure is planned to be included in our model through the Melosh rotation of the spins. [3]- References [1] W.R.B. dc Araujo, J.P.D.0 de Melo and T.Prederico, Phys. Rev. C52 (1995)2733. [2] II.Vogl and W. Weise, Prog. Burl. Part. Phys, 27 (1991) 195. [3] P.L.Chung and F. Coester, Phys. Rev. D44 (1991) 229. Deformed algebras and chiral symmetry breaking VARESE SALVADOR TIIVIOTEO, CELSO LUIZ LIMA IFUSP In the beginning of the sixties, Nambu and Jona-Lasinio proposed a model based in an analogy with the theory of superconductivity [1]. Originally the Nambu—jona- Lasinio model (NJL) was constructed as a pre-QCD theory of nucleons that interact via an effective twobody interaction. This model is reinterpreted today as a theory with quarks degrees of freedom. The Lagrangian of the NU model was constructed in such a way that the symmetries of QCD are also part of it. One of the most important of these symmetries is the chiral symmetry, which is essential to the understanding of the lightest hadrons and is spontaneously broken in QCD. The NIL model is very useful for observing how these things happen. In particular, the clynammic generation of fermion masses brought about by the breaking of chiral symmetry is one of the features of this model. Our porpose is to simulate the explicit chiral symmetry breaking by deforming the algebra of the model. This idea was motivated by recent applications of q-deformed algebras in nuclear structure problems. In this context, for instance, the pairing in a single j shell, the spectra of rotational nuclei and the phase transitions in the Lipkin model were studied [2]. 11
12 Interagio nucleon-nucleon - XX R2'FNB [1] Y. Namhu and G. Jona-Lasinio, Physical Review 122, 345 (1961). [2] D. Galetti, J. T. Lunar( B. M. Pi rnentel and C. L. Lima, Topics in Theoretical Physics, EFT (1995). Neutrino trapping in supernova shock wave generation H. RODRIGUES Centro Federal de Educagao Tecnolispica M. CHIAPPARINI Universidade do Estado do Rio di .lanciro S. B. DUARTE Ceram BrasileIn) de Peequisas Fisicas V. D'Av [LA. Observatorio Nacional - ON We investigate the effects of the neutrino trapping on the dynamical evolution of the supernova core collapse[1,2]. An equation of state of the cold hadronic stellar matter obtained from the relativistic mean lield theory explicitily including trapped neutrinos is applied[3,4]. An effective lagrangian description is used to the hydrodynamics of supernovae core, allowing us to calculate the intensity of the shock wave generated during the core-bounce. The basic characteristics of the supernova-core collapse, and the shock wave generated during the bounce, are reproduced. We discuss the neutrino trapping through its effect on the equation of state properties. [1]Ritchtinyer, R.D., "Difference Methods for Initial— Value Problem?, Interscience Publishers, Inc., New York (1957). [2]VonNeumann, J. e Richtmyer, R.D., J. Ap. Phys., 21 (1950), 232. [3]Rodrigues, 11., Duarte. S.B., Kodarna, T. e d'Avila, V., Astrophys. Spa. Sci., 194 (1992), 313. Rodrigues, R., Tee de Mestrado, CBPF(1989). [4]Zeldovich, Y.B. e Raiser, Y.P., "Physics of Shock Waves and High - Temoceatore llYclrodynarni Phenomena", Academic Press, Inc. (1970).
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