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Nous traitons trois problèmes liés à la fonction zêta de Riemann : 1) L'établissement de conditions pour déterminer l'alignement et la simplicité de la quasi-totalité des zéros d'une fonction de la forme f(s)=h(s)±h(2c-s), où h(s) est une fonction méromorphe et c un nombre réel. Cela passe par la généralisation du théorème d'Hermite-Biehler sur la stabilité des fonctions entières. Comme application, nous avons obtenu des résultats sur la répartition des zéros des translatées de la fonction zêta de Riemann et de fonctions L, ainsi que sur certaines intégrales de séries d'Eisenstein. 2) L'étude de la répartition des zéros des sommes partielles de la fonction zêta, et des ses approximations issues de la formule d'Euler-Maclaurin. 3) L'étude du prolongement méromorphe et de la frontière naturelle pour une classe de produits eulériens, qui inclut une série de Dirichlet utilisée dans l'étude de la répartition des valeurs de l'indicatrice d'Euler. / We deal with three problems related to the Riemann zeta function: 1) The establishment of conditions to determine the alignment and simplicity of most of the zeros of a function of the form f(s)=h(s)±h(2c-s), where h(s) is a meromorphic function and c a real number. To this end, we generalise the Hermite-Biehler theorem concerning the stability of entire functions. As an application, we obtain some results about the distribution of zeros of translations of the Riemann Zeta Function and L functions, and about certain integrals of Eisenstein series. 2) The study of the distribution of the zeros of the partial sums of the zeta function, and of some approximations issued from the Euler-Maclaurin formula. 3) The study of the meromorphic continuation and the natural boundary of a class of Euler products, which includes a Dirichlet series used in the study of the distribution of values of the Euler totient.

Neste trabalho, introduzimos a função zeta de Riemann \'ZETA\'(s), para s \'PERTENCE\' C \\ e apresentamos muito do que é conhecido como justificativa para a hipótese de Riemann. A importância de \'ZETA\' (s) para a teoria analítica dos números é enfatizada e fornecemos uma prova conhecida do Teorema dos Números Primos. No final, discutimos a importância de \'ZETA\'(s) para alguns modelos físicos de interesse e concluimos descrevendo como a hipótese de Riemann pode ser acessada estudando estes sistemas / In this work, we introduce the Riemann zeta function \'ZETA\'(s), s \'IT BELONGS\' C \\ and present much of what is known to support the Riemann hypothesis. The importance of \'ZETA\'(s) to the Analytic number theory is emphasized and a proof for the Prime Number Theorem is reviewed. In the end, we report on the importance of \'ZETA\'(s) to some relevant physical models and conclude by describing how the Riemann Hypothesis can be accessed by studying these systems

Neste trabalho, introduzimos a função zeta de Riemann \'ZETA\'(s), para s \'PERTENCE\' C \\ e apresentamos muito do que é conhecido como justificativa para a hipótese de Riemann. A importância de \'ZETA\' (s) para a teoria analítica dos números é enfatizada e fornecemos uma prova conhecida do Teorema dos Números Primos. No final, discutimos a importância de \'ZETA\'(s) para alguns modelos físicos de interesse e concluimos descrevendo como a hipótese de Riemann pode ser acessada estudando estes sistemas / In this work, we introduce the Riemann zeta function \'ZETA\'(s), s \'IT BELONGS\' C \\ and present much of what is known to support the Riemann hypothesis. The importance of \'ZETA\'(s) to the Analytic number theory is emphasized and a proof for the Prime Number Theorem is reviewed. In the end, we report on the importance of \'ZETA\'(s) to some relevant physical models and conclude by describing how the Riemann Hypothesis can be accessed by studying these systems

The thesis is in two parts. The first part is the paper “The Distribution of k-free integers” that my advisor, Dr. Roger Baker, and I submitted in February 2009. The reader will note that I have inserted additional commentary and explanations which appear in smaller text. Dr. Baker and I improved the asymptotic formula for the number of k-free integers less than x by taking advantage of exponential sum techniques developed since the 1980's. Both of us made substantial contributions to the paper. I discovered the exponent in the error term for the cases k=3,4, and worked the case k=3 completely. Dr. Baker corrected my work for k=4 and proved the result for k=5. He then generalized our work into the paper as it now stands. We also discussed and both contributed to parts of section 3 on bounds for exponential sums. The second part represents my own work guided by my advisor. I study the zeros of derivatives of Dirichlet L-functions. The first theorem gives an analog for a result of Speiser on the zeros of ζ'(s). He proved that RH is equivalent to the hypothesis that ζ'(s) has no zeros with real part strictly between 0 and ½. The last two theorems discuss zero-free regions to the left and right for L^{(k)}(s,χ).