We have applied the Meson Cloud Model (MCM) to calculate the charm and strange antiquark distribution in the nucleon. The resulting distribution, in the case of charm, is very similar to the intrinsic charm momentum distribution in the nucleon. This seems to corroborate the hypothesis that the intrinsic charm is in the cloud and, at the same time, explains why other calculations with the MCM involving strange quark distributions fail in reproducing the low x region data. From the intrinsic strange distribution in the nucleon we have extracted the strangeness radius of the nucleon, which is in agreement with other meson cloud calculations. Many years ago, it has been suggested by Sullivan [1] that some fraction of the nucleon's anti-quark sea distribution may be associated with non-perturbative processes like the pion * 1 cloud of the nucleon. The generalization of this process to other mesons is depicted in figs. 1a and b, and was used in refs. [2,3] to calculate the strange and anti-strange sea quark distributions in the nucleon.Recent analysis of deep inelastic neutrino-hadron scattering data [4] renewed the interest on the meson cloud picture of the nucleon. It is well known that, in this picture there is an asymmetry between sea quark and anti-quark momentum distributions [2]. This happens because the quark and the anti-quark are in different hadronic bound states. On the other hand, in extracting sea distributions from hard processes, it is usually assumed that the quark and antiquark sea contributions are equal. From the point of view of QCD, no definite statement on this subject can be made. Based on charge conjugation symmetry it is only possible to say that the quark sea distribution in the nucleon is equal to the antiquark sea distribution in the antinucleon. In ref. [4] it is shown that, in contrast to the meson cloud approach expectation, the sea strange and anti-strange quark distributions are quite similar. At first sight this would be a very strong argument against the relevance of the meson cloud [5]. The attempt to explain experimental data with the meson cloud model performed in refs. [2,3] has shown not only that the asymmetry present in this model seems to be in conflict with data but also that the calculated distributions are far below data for x < 0.3. However, in ref.[6], these data were reconsidered and combined with the CTEQ collaboration analysis [7]. The conclusion of the authors was that, considering the error bars, existing data do not exclude some asymmetry between the strange and anti-strange momentum distributions, which is significant only for x > 0.2 − 0.3.In the present work we apply the meson cloud model (MCM) to study strangeness and charm in the nucleon. In the case of strangeness, we shall try to extract some estimates on the strangeness radius of the nucleon. This is a very interesting quantity from both theoretical and phenomenological point of view. Indeed, approved parity-violating lepton scattering experiments at MIT-Bates [8] and CEBAF [9] will provide information on ...

We study contributions to the nucleon strange quark vector current form factors from intermediate states containing K * mesons. We show how these contributions may be comparable in magnitude to those made by K mesons, using methods complementary to those employed in quark model studies. We also analyze the degree of theoretical uncertainty associated with K * contributions.

The effects of short range correlations for two nucleon emission in peripheral relativistic heavy ion collisions are investigated. The cross section is calculated in Born approximation with properly orthogonalized initial and final states.

Resumo ','io mecanismo de "troca de fônon" de Feshbach e Zabek 1 é revisto e uma discussào detalhada é fornecida sobre o papel das leis de conservação e relação "tipo fônon" entre energia e momento transferidos. São investigados os efeitos de correlações de curto alcance na emissã.o de nucleons em colisões periféricas de íons pesados relativísticos. A seçã.o de choque é calculada na aproximação de Born. usando uma a.daptaçã.o conveniente do modelo de KaroF para o estado inicial e ondas planas, explicitamente ortogonalizadas ao estado inicial, para estados finais. Comparações com os resultados obtidos por Bertulani et a/. 3 usando ondas planas puras para. o estado final mostram que a ortogona.liza.çã.o desempenha um papel relevante no valor obtido para a seção de choque. Discute-se também a sensibilidade do resultado aos parâmetros usados na discussã.o do estado inicial.