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Physics in the year 2006 is tightly constrained by experiment, observation, and mathematical consistency. The Standard Model provides a remarkably precise de- scription of particle physics, and general relativity is quite successful in describing gravitational phenomena. At the same time, it is clear that a more fundamental theory is needed for several distinct reasons. Here we consider a new approach, which begins with the unusually ambitious point of view that a truly fundamental theory should aspire to explaining the origins of Lorentz invariance, gravity, gauge fields and their symmetry, supersymmetry, fermionic fields, bosonic fields, quantum mechanics and spacetime. The present dissertation is organized so that it starts with the most conventional ideas for extending the Standard Model and ends with a microscopic statistical picture, which is actually the logical starting point of the theory, but which is also the most remote excursion from conventional physics. One motivation for the present work is the fact that a Euclidean path integral in quantum physics is equivalent to a partition function in statistical physics. This suggests that the most fundamental description of nature may be statistical. This dissertation may be regarded as an attempt to see how far one can go with this premise in explaining the observed phenomena, starting with the simplest statistical picture imaginable. It may be that nature is richer than the model assumed here, but the present results are quite suggestive, because, with a set of assumptions that are not unreasonable, one recovers the phenomena listed above. At the end, the present theory leads back to conventional physics, except that Lorentz invariance and supersymmetry are violated at extremely high energy. To be more specific, one obtains local Lorentz invariance (at low energy compared to the Planck scale), an SO(N) unified gauge theory (with N = 10 as the simplest possibility), supersymmetry of Standard Model fermions and their sfermion partners, and other familiar features of standard physics. Like other attempts at superunification, the present theory involves higher dimensions and topological defects.

Orientador: Carola Dobrigkeit Chinellato / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-08T01:00:42Z (GMT). No. of bitstreams: 1 Rodrigues_JoaoPauloCaminhaCascudo_M.pdf: 7322384 bytes, checksum: e50136f5ec9d16fff8fd6a15ba64b5f0 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho estuda-se a propagação pelo meio intergaláctico de raios cósmicos ultra-energéticos partindo de fontes com distribuição espacial uniforme, considerando as perdas de energia ocasionadas pela expansão adiabática do universo e pelas interações com a Radiação , Cósmica de Fundo (produção de pares e-e+ e fotoprodução de píons), o que resulta no aparecimento do corte GZK (Greisen-Zatsepin-Kuzmin). A degradação de energia no espectro primário da radiação cósmica que chega ao topo da atmosfera terrestre é então analisada para diferentes redshifts das fontes injetoras. São utilizadas simulações de Monte Carlo bem como uma abordagem analítica, com a posterior comparação dos resultados obtidos em cada método. Uma vez conhecido o fluxo propagado, é feita uma estimativa da forma da resolução de energia do Observatório Pierre Auger, com a decorrente convolução desta resolução com o fluxo propagado, novamente utilizando-se ambos os métodos. Os resultados mostram que o corte GZK pode se mostrar severamente atenuado no fluxo convoluído, o que dificulta a sua constatação experimental / Abstract: In this work, we study the propagation of Ultra-High Energy Cosmic Rays (UHECR) which are injected into the intergalactic medium by sources with flat spatial distribution for several redshifts. The energy spectrum of UHECR observed on the Earth is directly influenced by the energy losses due to both the adiabatic expansion of the universe and interactions with the Cosmic Microwave Background radiation (e-e+ pair production and photoproduction of pions), which cause the so-called Greisen-Zatsepin-Kuzmin (GZK) cutoff. We perform Monte Carlo simulations and also consider a semi-analytical approach and compare the results obtained by each method. Once the propagated primary flux is known, we make a simple estimate of the shape of the Pierre Auger Observatory energy resolution. This resolution is folded with the propagated primary flux again utilizing both methods. The results show the GZK cutoff may be severely smeared and might not be detected as sharp as predicted. / Mestrado / Teorias Especificas e Modelos de Interação ; Sistematica de Particulas ; Raios Cosmicos / Mestre em Física