Discriminante dos corpos abelianos

Orientador: Paulo Roborto BrumattiTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação CientificaResumo: O cálculo do discriminante de um Corpo de Números K tem representado um grande desafio para muitos estudiosos e certamente a maior dificuldade consiste em se determinar uma base integral de K. Quando tal corpo K é abeliano pode-se recorrer ao Teorema de Kronecker- Weber que assegura que K está contido em alguma extensão ciclotômica Q((m) e, neste caso, pode-se usar a Fórmula do Condutor-Discriminante para calcular o discriminante de K. Os resultados aqui obtidos visam o cálculo efetivo dos Discriminantes dos Corpos de Números Abelianos e faz-se o uso pleno da Fórmula do Condutor-Discriminante, isto é, o discriminante de um corpo K é, a menos de sinal, o produtório dos condutores dos caracteres associados a K. Quando o condutor de K é uma potência de primo, ou seja, K ç Q( (pr) para algum primo p e r um inteiro positivo, então o discriminante de K é uma função do seu grau, quando o primo é ímpar; e tal fórmula é dada pelo Teorema 3.1. Quando tal primo é 2, o Teorema 3.3 determina o discriminante de K, distinguindo os casos em que K é um Corpo Ciclotômico e quando não é. O caso geral foi abordado no Teorema 3.4 e descreve o discriminante de um Corpo de Números Abeliano qualquer, em função do seu grau, do seu condutor e dos graus de subcorpos particulares de KAbstract: The computation of the discriminant of a number field K has represented a great challenge to number theorists, and certainly the difficulty lies in determining an integral basis for K. "When K is Abelian, one can resort to the Kronecker- Weber theorem, which guarantees that K is contained in some cyclotomic field Q( (m). ln this case, one can use the conductor-discriminant formula for evaluating the discriminant of K. The results obtained here aim at efficiently computing the discriminant of any Abelian number field. For that, we wiIl fully use the conductor-discriminant formula, which states that the discriminant of a field K is the product of the conductors of the characters associated to K. "When the conductor of K is a power of an odd prime p, that is, K ç Q((pr) for some positive integer r, then the discriminant of K is a function of its degree only - see the formula given in Theorem 3.1. When p = 2, Theorem 3.3 provides a formula for the discriminant of K which consists of two expressions, depending on whether K is a cyclotomic field. The general case is addressed in Theorem 3.4. lt gives the discriminant of any Abelian number field as a function of its degree, its conductor, and the degrees of some particular subfields of KDoutoradoDoutor em Matemátic

On Computing Discriminants of Subfields of Q(ζpr)

AbstractThe conductor–discriminant formula, namely, the Hasse Theorem, states that if a number field K is fixed by a subgroup H of Gal(Q(ζn)/Q), the discriminant of K can be obtained from H by computing the product of the conductors of all characters defined modulo n which are associated to K. By calculating these conductors explicitly, we derive a formula to compute the discriminant of any subfield of Q(ζpr), where p is an odd prime and r is a positive integer

On computing discriminants of subfields of ℚ (ζp r)

The conductor-discriminant formula, namely, the Hasse Theorem, states that if a number field K is fixed by a subgroup H of Gal(ℚ(ζn)/ℚ), the discriminant of K can be obtained from H by computing the product of the conductors of all characters defined modulo n which are associated to K. By calculating these conductors explicitly, we derive a formula to compute the discriminant of any subfield of ℚ(ζpr), where p is an odd rime and r is a positive integer. © 2002 Elsevier Science USA

Two matrix-based lattice construction techniques

Let m and n be integers greater than 1. Given lattices A and B of dimensions m and n, respectively, a technique for constructing a lattice from them of dimension m+n-1 is introduced. Furthermore, if A and B possess bases satisfying certain conditions, then a second technique yields a lattice of dimension m+n-2. The relevant parameters of the new lattices are given in terms of the respective parameters of A,B, and a lattice C isometric to a sublattice of A and B. Denser sphere packings than previously known ones in dimensions 52, 68, 84, 248, 520, and 4098 are obtained. © 2012 Elsevier Inc. All rights reserved