Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

Η μελέτη της διπλής διάσπασης βήτα έχει πρωτεύουσα σπουδαιότητα για τη φυσική των νετρίνων. Θεωρείται ως ο καλύτερος τρόπος για να εξεταστεί ο θεμελιώδης χαρακτήρας των νετρίνων και να καθοριστεί η μάζα τους. Από πειραματικής πλευράς περίπου εννέα διαφορετικού τύπου ισότοπα χρησιμοποιούνται στα πειράματα. Μετά από μια γενική εισαγωγή ακολουθεί μια σύντομη συζήτηση σχετικά με τη φυσική των νετρίνων και της παρουσίας τους στις β διασπάσεις. Η πειραματική προσέγγιση, οι δυσκολίες που αντιμετωπίζουμε καθώς και η τρέχουσα πειραματική κατάσταση στις διπλές βήτα διασπάσεις συζητιούνται, ακολουθούμενες από μια σύντομη συζήτηση των ιδεών και των προτάσεων των μελλοντικών πειραμάτων που σχεδιάζονται. / Double beta decay research has a major role in neutrino physics. It is considered the best way to examine the nature of neutrinos and to determine their mass. From an experimental point of view, nine different isotopes are being used in the experiments. After a general introduction, a brief discussion about neutrino physics and their role in beta decays will follow. The experimental approach, the difficulties that we face and the current double beta decay experiments will be discussed, followed by another summary of the ideas and the proposals of the future experiments.

Next-generation cosmological surveys will demand an unprecedented understanding of the interplay between theoretical and observational aspects of weak gravitational lensing. This thesis presents a study of the parameter degeneracies and theoretical uncertainties which will affect weak lensing tests of cosmology beyond the standard paradigm. In particular, tests of alternative theories of gravity and of spatial curvature are considered. First, by considering linear-order departures from the standard gravitational theory of general relativity, a novel expression is derived for the weak lensing convergence power spectrum under alternative theories of gravity. Using this expression, degeneracies between gravitational parameters in weak lensing observations are explored, first with a focus on scale-independent parameterisations of gravity, then considering new physical scales introduced by alternative theories. The degeneracy-breaking offered by the combination of weak lensing and redshift-space distortions is shown to be robust to the time-dependence of the functions parameterising modified gravity. Next, the gravity-testing statistic EG is investigated, and a new theoretical expression for its observationally-motivated definition is presented. The theoretical uncertainty of EG is compared to forecast statistical errors, and found to be significant in the case of a more futuristic measurement. Predictions are then computed for EG under deviations from general relativity, and the ongoing utility of EG as a probe of gravity is discussed. Finally, an investigation is made of the potential for measuring or constraining the spatial curvature using weak lensing and complementary observables. The predicted constraint on the spatial curvature is forecast for a suite of upcoming surveys, and the effect of including parameters which may be degenerate with the spatial curvature is explored. It is found that upcoming observations are likely to constrain spatial curvature at a 10⁻³ level, but not to reach the best-case constraint of ~10⁻⁴.

Orientador: Juan Carlos Montero Garcia. / Banca: Dionísio Bazeia Filho / Banca: Renata Zukanovich Funchal / Banca: Rogério Rosenfeld / Banca: Oscar José Pinto Éboli / Doutor

The neon-sodium cycle (NeNa cycle) of hydrogen burning is active in stars of the Asymptotic Giant Branch, in classical novae, and in supernovae of type Ia. The thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction is determined by a large number of resonances, and it represents the most uncertain rate in the NeNa cycle. This PhD thesis reports on an experiment to study tentative 22Ne(p,γ)23Na resonances at Elab = 71 and 105 keV, as well as the direct capture component of the reaction rate for Elab ≤ 400 keV. The measurements were performed deep underground at the Laboratory for Un- derground Nuclear Astrophysics - LUNA (Gran Sasso, Italy), taking advantage of the strong reduction in the cosmic ray induced background. The LUNA-400-kV electrostatic accelerator and a differentially pumped, windowless gas target of iso- topically enriched 22Ne gas were used. The γ-rays from the reaction were detected with a 4π bismuth germanate scintillator. The data show upper limits on the strengths of the resonances at Elab = 71 and 105 keV of 5.8 × 10−11 and 7.0 × 10−11 eV respectively. The resonances at Elab = 156.2, 189.5 and 259.7 keV have been re-studied and show 20% higher strength than the literature. The present experiment did not show any evidence for the direct capture process at the low energies studied. In addition to the experimental work at LUNA, the 3He(α, γ)7Be and 7Be(p, γ)8B reactions were studied using the most recent solar neutrino data available. Based on the standard solar model and the experimentally measured fluxes of solar 7Be and 8B neutrinos, the astrophysical S-factors of both reactions were evaluated directly in the solar Gamow peak.

No description available.

Os aglomerados de galáxias são as maiores estruturas gravitacionais em situação de quase-equilíbrio, mas apesar dos esforços de pesquisa das últimas décadas, pouco conhecemos de suas estruturas e composição. Os recentes avanços teóricos e observacionais associados aos aglomerados de galáxias motivam essa proposta de pesquisa. Nosso foco é no entendimento da componente não-observada em aglomerados de galáxias. Especificamente, investigamos uma teoria de gravitação alternativa denominada Gravitação Newtonina Modificada (MOND) que pretende substituir o paradigma da matéria escura, mas que apresenta problemas quando aplicada aos centros dos aglomerados. Revisamos e sintetizamos o estado da arte na modelagem da Matéria Escura no centro desses objetos e testamos, em especial, uma proposta de solução dos problemas da MOND: a inclusão de neutrinos massivos. Ao mesmo tempo que testamos a teoria MOND + v,fazemos uma análise critica de como os limites às massas de neutrino são obtidos a partir de aglomerados. / Clusters of galaxies are the largest structures in the universe in a quasi-equilibrium state, but, despite research efforts in the past decades, their structure and composition are still poorly understood. Recent theoretical and abservational advances in the understanding of these structures motivate the present research work. Our focus lies on the understanding of the non-luminous component af galaxy clusters. Specifically, we investigate an alternative gravitational theory named MOND, or Madified Newtonian Dynamics, which aims at replacing the dark matter (DM) paradigm, but presents problems when applied to the centers of galaxy clusters. We have reviewed and summarized the state of the art on the modeling of the dark matter in the centers of clusters of galaxies and tested a proposal of solution: the inclusion of massive neutrinos in the MOND scenario. Besides testing MOND + v, we have analised how limits are imposed on the neutrino mass via the study of clusters of galaxies.

xix, 149 p. ; ill. (some col.) A print copy of this title is available through the UO Libraries. Search the library catalog for the location and call number. / We report on a study of the invariant mass spectrum of the hadronic system in à - [arrow right] à - à 0 à à à à à ½ à decays. This study was performed using data obtained with the BABAR detector operating at the PEP-II e + e - collider. We present fits to phenomenological models in which resonance parameters associated with the à (770), à '(1450) and à "(1700) mesons are determined. We also discuss the implications of our data with regard to estimates of the hadronic contribution to the muon anomalous magnetic moment. / Adviser: Eric Torrence

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Física / Made available in DSpace on 2013-03-04T18:37:06Z (GMT). No. of bitstreams: 1 304965.pdf: 2141786 bytes, checksum: 57d87045370f972d6d105eae421eee84 (MD5) / Acredita-se que uma protoestrela de nêutrons nasça partir do colapso do núcleo de uma estrela massiva em conjunção com uma explosão de supernova. Durante os primeiros segundos de evolução, aproximadamente toda energia de ligação é irradiada em forma de neutrinos. A luminosidade de neutrinos é controlada por vários fatores, alguns deles sendo a massa total da protoestrela de nêutrons e a opacidade dos neutrinos em relação a sua matéria constituinte. Nesta tese mostramos que há uma diferença importante na evolução de protoestrelas de nêutrons quando estas apresentam a formação da pasta nuclear na sua crosta. A fase de desleptonização e resfriamento no início da vida da protoestrela de nêutrons é temporalmente mais longa em comparação com uma protoestrela de nêutrons constituída apenas de matéria homogênea. Isso pode ser dito porque os coeficientes de difusão das equações de transporte que regem os processos de desleptonização e resfriamento da estrela são sempre menores na presença da pasta nuclear. A pasta nuclear foi calculada pelo método de coexistência de fases impondo neutralidade de carga, equilíbrio beta e aprisionamento de neutrinos. O coeficiente da energia de superfície nuclear foi calculado a partir de três parametrizações diferentes e vimos que, com uma das parametrizações, os resultados obtidos se aproximam muito da pasta nuclear calculada pelo método de Thomas-Fermi, o que confere credibilidade ao método aqui utilizado. / A protoneutron star is believed to be born from the collapse of a very massive star and a supernova explosion. During the first few seconds of the star evolution, almost all the binding energy is taken away by the neutrinos. The neutrino luminosity is controlled mainly by the total protoneutron star mass and the neutrino opacity. In this thesis we show that an important difference in the evolution of a protoneutron star is seen if a pasta phase is present in its inner crust. The deleptonization and cooling processes take longer than if the crust would be made of homogeneous matter only. This statement results from the smaller difusion coefficients obtained with the inclusion of the pasta phase. The difusion coefficients present in the transport equations determine the temporal behavior associated with the deleptonization and cooling processes. The nuclear pasta was calculated by the coexistence phases method. We have assumed total charge neutrality, b -equilibrium and neutrino trapping in the equation of state. The surface energy coefficient was obtained with three different parametrizations and one of them pratically reproduces results obtained with the more sophisticated Thomas-Fermi method, yieldind credibility to our method.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Física. / Made available in DSpace on 2013-03-04T20:15:22Z (GMT). No. of bitstreams: 1 305338.pdf: 862756 bytes, checksum: f7d8856e929eab0f2285b61f2ff81aee (MD5) / Estamos interessados em estudar o comportamento dos neutrinos e suas propriedades em um meio nuclear denso. O meio nuclear será descrito pelo modelo de Walecka não linear, onde usamos a aproximação de campo médio para a solução do mesmo. Além de mésons, nucleons e léptons, incluímos os bósons fracos neutro Z e carregados W+ e W- no modelo, calculando propriedades do sistema, como a densidade de energia, pressão e fração de partículas. Obtemos também a seção de choque total e o livre caminho médio dos neutrinos, levando em conta tanto espalhamentos, mediados pelo bóson fraco neutro, quanto absorção de neutrinos pelo meio, mediado pelos bósons carregados. Comparamos então o resultado para duas parametrizações diferentes para a interação forte: uma onde a não linearidade é introduzida explicitamente e os acoplamentos são definidos por constantes e outra onde tais constantes passam a depender da densidade. A solução desse problema tem interesse direto em simulações para a perda de neutrinos no momento da formação de uma estrela de nêutrons a partir da explosão de uma supernova. / The behavior and properties of neutrinos in dense nuclear matter is studied. The nuclear matter itself is described by the non-linear Walecka model, solved in the mean-field approximation. Besides the nucleons, mesons and leptons, the weak neutral boson and the weak charged bosons are included in the model and the energy density, pressure and particle fractions are calculated. We also obtain the total cross-section and mean-free path for the neutrinos, taking into account scattering and neutrino absorption. We compare the final results for two know kinds of model parametrizations: one in which nonlinear effects in the strong sector are explicitly written in the model Lagrangian and another one in which the coupling constants are density dependent. The solution for this problem is interesting for the understanding of neutrino diffusion in a newly born neutron star after a supernova explosion.