In this work we study the effect of the accretion of dark matter into neutron stars. We have considered two relativistic nuclear effective models for the structure of neutron stars (ZM and Boguta-Bodmer) and three profiles for dark matter (Navarro-Frenk-White, Einasto, and Burkert). We have analyzed the effects of these effective models and profiles in the equation of state of nuclear matter and in the capture rate of dark matter by neutron stars. Our results confirm that the capture rate of dark matter by neutron stars is strongly model dependent. This leads to more questions than answers due to the uncertainties in the significance of the results, requiring therefore for its elucidation new signatures of capture of dark matter by these stellar objects.

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The role of many-body correlations (many-body forces) and K − -K 0 condensation in β-equilibrated hyperonic matter is investigated in order to shed some light in the hyperonization puzzle, ie that neutron star mass of 2M cannot be obtained in the presence of exotic degree of freedoms. In this investigation, we use an effective relativistic QHD-model with parameterized couplings which represents an extended compilation of other effective models found in the literature. Our theoretical approach exhausts the whole fundamental baryon octet (n, p, Σ − , Σ 0 , Σ + , Λ, Ξ − , Ξ 0 ) and simulates n-order corrections to the minimal Yukawa couplings by considering many-body nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (σ, σ * ), vector-isoscalar (ω, φ), vector-isovector ( ), and scalar-isovector (δ) sectors. Following recent experimental results, we consider in our calculations the extreme case where the Σ − experiences such a strong repulsion that its influence in the nuclear structure of a neutron star is excluded at all. We study the effects of this exclusion on the phase transition of conventional exotic hadronic matter to hadronic matter containing a condensate of kaons and anti-kaons. As a novelty in the treatment of kaon and anti-kaon condensation in high density nuclear matter, we consider a Lagrangian formulation which describes, in addition to the interaction involving baryons and mesons and the contribution of kaons and anti-kaons in free propagation, the presence of many-body forces involving kaon, anti-kaon and meson fields. To implement the corresponding phase transition we considered the Gibbs conditions combined with the mean-field approximation, giving rise to a mixed phase of coexistence between baryon matter and the condensed of kaons and anti-kaons. Our investigation show that even with kaon condensation, the nuclear equation of state satisfies both the maximum mass and the allowed ranges of mass and radius of neutron stars.

pela incansável e valiosa orientação e principalmente pelo apoio, amizade e confiança, sem os quais esse trabalho não teria sido realizado. À Dra. Maria Inês B. Bernardi, pela amizade, apoio e imprescindível contribuição ao trabalho. Ao Prof. Dr. José A. Eiras, pela disposição dos laboratórios e equipamentos do Grupo de Cerâmicas Ferroelétricas. À Profa. Dra. Márcia R. Gallas, pela sinterização das amostras cerâmicas em alta pressão. Ao Dr. Manuel H. Lente, pela caracterização dielétrica e pelas valiosas discussões. Ao Prof. Dr. Paulo S. Pisani, pela caracterização por espectroscopia Raman. Ao Prof. Dr. Fenelon M. L. Pontes, pelo auxílio na preparação de amostras na forma de filmes finos. À Profa. Dra. Dulcinei Garcia, pela colaboração nas discussões sobre o processo de sinterização.

We investigate the role of many-body correlations in the maximum mass of neutron stars using the effective relativistic QHD-model with parameterized couplings which represents an extended compilation of other effective models found in the literature. Our model exhausts the whole fundamental baryon octet (n, p, Σ − , Σ 0 , Σ + , Λ, Ξ − , Ξ 0 ) and simulates corrections to the minimal Yukawa couplings by considering many-body nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (σ, σ * ), vector-isoscalar (ω, φ), vector-isovector ( ) and scalar-isovector (δ). Following recent experimental results, we consider in our calculations the extreme case where the Σ − experiences such a strong repulsion that it does not appear at all in nuclear matter.