Let K be the function field of an irreducible, smooth projective curve X defined over Fq. Let [lemniscate] be a fixed point on X and let A [a subset of or is equal to] K be the Dedekind domain of functions which are regular away from [lemniscate]. Following the work of Greg Anderson, we define special polynomials and explain how they are used to define an A-module (in the case where the class number of A and the degree of [lemniscate] are both one) known as the module of special points associated to the Drinfeld A-module [rho]. We show that this module is finitely generated and explicitly compute its rank. We also show that if K is a function field such that the degree of [lemniscate] is one, then the Goss L-function, evaluated at 1, is a finite linear combination of logarithms evaluated at algebraic points. We conclude with examples showing how to use special polynomials to compute special values of both the Goss L-function and the Goss zeta function.

Let k be the algebraic closure of the field with q elements. We build upon recent work of Ulmer and Berger to give examples of elliptic curves and higher dimensional abelian varieties over the field K=k(t) with the property that their ranks become arbitrarily large when dth roots of the variable t are adjoined to K for d varying across the integers relatively prime to q. We also give a first example of an elliptic curve whose rank under such extensions grows linearly in d, for those d prime to q.

Let $E$ be an elliptic curve over the rationals without complex multiplication such that any elliptic curve $\mathbb{Q}$-isogenous to $E$ has trivial $\mathbb{Q}$-torsion. Koblitz conjectured that the number of primes less than $x$ for which $|E(\mathbb{F}_p)|$ is prime is asymptotic to $$C_E\frac{x}{(\log{x})^2} $$ for $C_E$ some constant dependent on $E.$ Miri and Murty showed that for infinitely many $p,$ $|E(\mathbb{F}_p)|$ has at most 16 prime factors using the lower bound sieve and assuming the Generalized Riemann Hypothesis. This thesis generalizes Koblitz's conjectures to a function field setting through Drinfeld modules. Let $\phi$ be a Drinfeld module of rank 2, and $\mathbb{F}_q$ a finite field with every $\mathbb{F}_q[t]$-isogeny having no $\mathbb{F}_q[t]$-torsion points and with $\text{End}_{\overline{k}}(\phi)=\mathbb{F}_q[t].$ Furthermore assume that for each monic irreducible $l\in \mathbb{F}_q[t],$ the extension generated by adjoining the $l$-torsion points of $\phi$ to $\mathbb{F}_q(t)$ is geometric. Then there exists a positive constant $C_{\phi}$ depending on $\phi$ such that there are more than $$ C_{\phi}\frac{q^x}{x^2}$$ monic irreducible polynomials $P$ with degree less then $x$ such that $\chi_{\phi}(P)$ has at most 13 prime factors. To prove this result we develop the theory of Drinfeld modules and a translation of the lower bound sieve to function fields.

Let $E$ be an elliptic curve over the rationals without complex multiplication such that any elliptic curve $\mathbb{Q}$-isogenous to $E$ has trivial $\mathbb{Q}$-torsion. Koblitz conjectured that the number of primes less than $x$ for which $|E(\mathbb{F}_p)|$ is prime is asymptotic to $$C_E\frac{x}{(\log{x})^2} $$ for $C_E$ some constant dependent on $E.$ Miri and Murty showed that for infinitely many $p,$ $|E(\mathbb{F}_p)|$ has at most 16 prime factors using the lower bound sieve and assuming the Generalized Riemann Hypothesis. This thesis generalizes Koblitz's conjectures to a function field setting through Drinfeld modules. Let $\phi$ be a Drinfeld module of rank 2, and $\mathbb{F}_q$ a finite field with every $\mathbb{F}_q[t]$-isogeny having no $\mathbb{F}_q[t]$-torsion points and with $\text{End}_{\overline{k}}(\phi)=\mathbb{F}_q[t].$ Furthermore assume that for each monic irreducible $l\in \mathbb{F}_q[t],$ the extension generated by adjoining the $l$-torsion points of $\phi$ to $\mathbb{F}_q(t)$ is geometric. Then there exists a positive constant $C_{\phi}$ depending on $\phi$ such that there are more than $$ C_{\phi}\frac{q^x}{x^2}$$ monic irreducible polynomials $P$ with degree less then $x$ such that $\chi_{\phi}(P)$ has at most 13 prime factors. To prove this result we develop the theory of Drinfeld modules and a translation of the lower bound sieve to function fields.

Traditionally number theorists have studied, both theoretically and computationally, elliptic curves and their L-functions over number fields, in particular over the rational numbers. Much less work has been done over function fields, especially computationally, where the underlying geometry of the function field plays an intimate role in the arithmetic of elliptic curves. We make use of this underlying geometry to develop a method to compute the L-function of an elliptic curve and its twists over the function field of the projective line over a finite field. This method requires computing the number of points on an elliptic curve over a finite field, for which we present a novel algorithm. If the j-invariant of an elliptic curve over a function field is non-constant, its L-function is a polynomial, hence its analytic rank and value at a given point can be computed exactly. We present data in this direction for a family of quadratic twists of four fixed elliptic curves over a few function fields of differing characteristic. First we present analytic rank data that confirms a conjecture of Goldfeld, in stark contrast to the corresponding data in the number field setting. Second, we present data on the integral moments of the value of the L-function at the symmetry point, which on the surface appears to refute random matrix theory conjectures. / text

In this thesis, we give two simple and effective methods for constructing Kummer extensions of algebraic function fields over finite fields with many rational places. Some explicit examples are obtained after a practical search. We also study fibre products of Kummer extensions over a finite field and determine the exact number of rational places. We obtain explicit examples with many rational places by a practical search. We have a record (i.e the lower bound is improved) and a new entry for the table of van der Geer and van der Vlugt.

Orientador: Sueli Irene Rodrigues Costa / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica / Made available in DSpace on 2018-08-23T07:10:07Z (GMT). No. of bitstreams: 1 Ferreira_Jamil_D.pdf: 1528200 bytes, checksum: a1ca349425c4bcf544a36d17d3157b3c (MD5) Previous issue date: 2013 / Resumo: O número de classes de divisores de grau zero, h, de corpos de funções algébricas elípticos e hiperelípticos desempenha papel importante nos esquemas criptográficos baseados em curvas elípticas e hiperelípticas. Nesse contexto, h é um número grande e é usualmente procurado por meio de algoritmos (baby step - giant step, por exemplo) em um intervalo de números reais obtido após um truncamento no produto infinito de Euler da função zeta do corpo de funções. Tendo a desigualdade de Hasse-Weil como motivação, encontramos identidades finitas para h que são também explícitas no sentido de que seus custos computacionais são diretamente deduzíveis dessas identidades. Como consequência, obtivemos também identidades finitas e explícitas para os coeficientes ai do L-polinômio da função zeta. Ferramentas fundamentais nesta pesquisa foram as L-séries de Artin e outros resultados envolvendo os símbolos polinomiais de Legendre / Abstract: The divisor class number of degree zero, h, of elliptic and hyperelliptic function fields plays an important role in cryptographic schemes based on elliptic and hyperelliptic curves. In this context, h is a large number and it is usually searched by means of algorithms (baby step - giant step, for example) in an interval of real numbers obtained after truncating the infinit Euler product coming from the zeta function of the function field. Taking the Hasse-Weil inequality as motivation, we derived finite identities for h which are also explicit in the sense that their computational costs are straightforwardly derivable from these identities. We also obtained finite and explicit identities for the coefficients ai of the L-polynomialof the zeta function. Fundamental tools for this research were the Artin L-series and other results involving the Legendre polynomial symbols / Doutorado / Matematica / Doutor em Matemática

Submitted by Renata Lopes (renatasil82@gmail.com) on 2016-01-13T13:41:39Z No. of bitstreams: 1 marianadealmeidanerycoutinho.pdf: 1084614 bytes, checksum: dded13e49c590fa1685ce4a2b9e5cf3c (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2016-01-25T17:33:13Z (GMT) No. of bitstreams: 1 marianadealmeidanerycoutinho.pdf: 1084614 bytes, checksum: dded13e49c590fa1685ce4a2b9e5cf3c (MD5) / Made available in DSpace on 2016-01-25T17:33:13Z (GMT). No. of bitstreams: 1 marianadealmeidanerycoutinho.pdf: 1084614 bytes, checksum: dded13e49c590fa1685ce4a2b9e5cf3c (MD5) Previous issue date: 2015-03-10 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / O estudo das curvas algébricas sobre corpos finitos, o qual está intrinsecamente relacionado à teoria dos corpos de funções sobre corpos finitos, é de grande interesse na álgebra abstrata, com destaque para aplicações na teoria dos números e na teoria dos códigos. Com essa motivação, estamos aqui interessados em estudar a existência de corpos de funções F/Fq com um número prescrito de lugares de determinados graus, estando baseados em algumas seções do artigo de ANBAR e STICHTENOTH (2013). Para isso, faremos também uma abordagem acerca da teoria geral dos corpos de funções, apresentando os principais elementos que nos auxiliarão na compreensão dos resultados anteriormente mencionados. / The study of algebraic curves over finite fields, which is intrinsically related to the theory of function fields over finite fields, is of great interest in abstract algebra, especially for applications in number theory and coding theory. With this motivation, we are here interested in studying the existence of function fields with a prescribed number of places of certain degrees, based on some sections of the paper of ANBAR and STICHTENOTH (2013). For this, we will also make a study of the general theory of function fields, showing the main elements that will assist us in understanding the results mentioned above.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: It is well known that the ring of integers Z and the ring of polynomials A = Fr[T] over a finite field Fr have many properties in common. It is due to these properties that almost all the famous (multiplicative) number theoretic results over Z have analogues over A. In this thesis, we are devoted to utilising this analogy together with the theory of Carlitz modules. We do this to survey and compare the analogues of cyclotomic polynomials, the size of their coefficients and cyclotomic extensions over the rational function field k = Fr(T). / AFRIKAANSE OPSOMMING: Dit is bekend dat Z, die ring van heelgetalle en A = Fr[T], die ring van polinome oor ’n eindige liggaam baie eienskappe in gemeen het. Dit is as gevolg van hierdie eienskappe dat feitlik al die bekende multiplikative resultate wat vir Z geld, analoë in A het. In hierdie tesis, fokus ons op die gebruik van hierdie analogie saam met die teorie van die Carlitz module. Ons doen dit om ’n oorsig oor die analoë van die siklotomiese polinome, hul koëffisiënte, en siklotomiese uitbreidings oor die rasionele funksie veld k = Fr(T).

A Teoria das curvas algébricas sobre corpos finitos é de fundamental importância para a matemática e tem aplicações essenciais em muitas áreas, tais como Geometria Finita, Teoria dos Números, Teoria de Grafos e Teoria de Códigos. Neste trabalho tratamos do segmento algébrico desta teoria, isto é, corpos de funções algébricas, inicialmente sobre qualquer corpo, apresentando propriedades fundamentais. Depois nos restringimos aos corpos de funções algébricas sobre corpos finitos, e são apresentados resultados referentes à estimativa do gênero e número de lugares racionais, além de propriedades que conectam estes dois números e a característica do corpo, sendo o principal resultado dado por: Para q uma potência de um número primo e N inteiro não negativo, existe uma constante inteira não negativa g0 (dependendo de q e N) tal que, para todo g maior ou igual a \'g IND. 0\', existe um corpo de funções sobre \'F IND. q\' de gênero g tendo exatamente N lugares racionais / The Theory of algebraic curves over finite fields is of fundamental importance to mathematics and has essential applications in many areas, such Finite Geometry, Number Theory, Graph Theory and Coding Theory. In this work we treat the algebraic part of this theory, ie, algebraic function fields, initially over any field, presenting fundamental properties. Then we restrict to algebraic function fields over finite fields, and presented results for the estimation of the genus and the number of racional places, as well as properties that connect these two numbers and the characteristic of the constant field, being the main result given by: For q a prime power and N a non-negative integer, there is an integer non-negative \'g IND. 0\' (that depends of q and N) such that for all \'g > or =\' \'g IND. 0\' , there exists a function field over \'F IND. q\' with genus g having exactly N racional places