Unidades Hipercentrais em Anéis de Grupo. / Hypercentral units in group rings
AUTOR(ES)
Edson Ryoji Okamoto Iwaki
DATA DE PUBLICAÇÃO
2000
RESUMO
A great deal of problems in Group Rings centralize around the study of its group of units. Hence it becomes important to know the structure of the group of units U(ZG). But with a few exceptions, we do not have much information about its structure. Trying to obtain more information about the structure of U(ZG), we could, for example, study the upper central series of U(ZG). In case G is finite, a result of Gruenberg implies that U(ZG) has finite central height. This fact allow us to study the hypercenter of U(ZG). In order to obtain more information about the hypercentral units of U(ZG) we need a description of the torsion subgroup of the hypercenter of U(ZG) which is provided by results of Bovdi on periodic normal subgroups of U(ZG). Gruenbergs result suscites some questions which we will try to answer in this work. Among them: The upper bound for the upper central serie of U(ZG) depends on of the group G? How could we determine the central height of U(ZG)? It is interesting to see how we could obtain an estimative for the central height of U(ZG) using the Normalizer Conjecture. All these questions are answered in chapter 4, as a consequence of Arora, Hales and Passis work which guarantees us that in this case the central height of U(ZG) is at most 2. Nevertheless this result of Arora, Hales and Passi doesnt use the Normalizer Conjecture, we suppose here that the Normalizer Conjecture holds and used a result of Gross to obtain estimatives to the central height of U(ZG). Our aim was to connect the question discussed ahead with a intensive research problem, the Normalizer Conjecture. This arises the following question: For which groups does U(ZG) have central height exactly 0, 1 or 2? This question is also answered by Arora, Hales and Passi. Finally, another result of Arora, Hales and Passi present us a characterization of the hypercenter of U(ZG), which surprisingly satisfies the condition presented in the Normalizer Conjecture. It is interesting to observe here the appearing of Normalizer Conjecture to obtain an estimative for the central height of U(ZG) and to obtain a characterization of the hypercenter of U(ZG). In chapter 5 we present a result of Li which generalizes the result of Arora, Hales and Passi to the case when G is a periodic group. He proves that the central height of U(ZG) is also at most 2. Introducing the concept of n-center he was able to use the results about the hypercenter of U(ZG) to obtain a characterization of the n-center of U(ZG).
ASSUNTO(S)
hypercentre unidade anel de grupo normalizer hipercentro normalizador group ring unit
