Mathematical Sciences: Superstability in Model Theory

Ambar Chowdhury， U. Connecticut分类理论关注的是确定给定的一类数学对象是否允许“结构理论”。在最好的情况下，结构理论分配了一定的维度，这些维度决定了类中的每个对象直到同构。给定域上的向量空间类，具有通常的维数概念，是一个很好的例子。更一般地说，结构理论旨在描述类的每个成员是如何从同一个类中的较小对象构建而成的，或者甚至是从属于第二个被很好理解的类的更简单的对象构建而成的。Shelah孤立了可数完备一阶理论的某些性质，这些性质是T的类模型承认结构理论的充分必要条件。一个关键的性质是超稳定，它保证了T的模型的某些子集可以被看作是预先几何，因此具有所需的维数。调查上述预言的确切性质，以及它们相互作用的方式，可以获得关于模型精细结构的非常深刻的信息；这种研究被称为几何稳定性理论。Chowdhuiy将运用几何稳定性理论的方法来进一步了解超稳定理论。特别是，他的工作旨在将希拉的分类结果扩展到不可数理论。这将导致关于超稳定理论模型的新结构信息，无论可数与否。此外，乔杜里计划研究超稳定理论的哪些性质可以推广到一个更广泛的类别，即超简单理论。超简单理论虽然不一定稳定，但却表现出了超稳定理论的一些重要特征。在模型理论中，人们研究那些满足给定公理集合的数学对象（称为“模型”）。虽然人们可能会认为群是特定物体（如有机分子）的变换或对称的集合，但被称为群的一般物体类别恰恰是三个群公理的模型。在代数中，人们试图理解复杂的对象（例如，群体）是如何从已经理解的对象中构建出来的；当这种理论成立时，就被称为“结构理论”。在模型论中，人们考虑一组一般的公理和一组模型，并询问在这组公理中是否存在保证结构理论存在的固有性质。值得注意的是，一组公理的某些抽象性质确实暗示了相应对象的某些结构特征；其中一种特性被称为“超稳定性”。首席研究员建议继续研究超稳定性（及其变化）及其对更广泛对象的结构含义，其中包括有趣和重要的数学类。

Abstract DMS 9626112 Ambar Chowdhury, U. Connecticut Classification theory is concerned with determining whether a given class of mathematical objects admits a "structure theory". In the best cases, a structure theory assigns certain dimensions which determine each object in the class up to isomorphism. The class of vector spaces over a given field, with the usual notion of dimension, is a simple example of a good case. More generally a structure theory aims to describe how each member of the class is built from smaller objects in the same class, or even from simpler objects belonging to a second, well understood class. Shelah has isolated certain properties of a countable, complete first order theory which are necessary and sufficient for the class models of T to admit a structure theory. One key property is that of being superstable, a guarantee that certain subsets of the models of T can be viewed as pregeometries, and thus carry the desired dimensions. Investigating the precise nature of the aforementioned pregeometries, and the way in which they interact, can yield very deep information about the fine structure of the models; such investigation has become known as geometric stability theory. Chowdhuiy will apply the methods of geometric stability theory to gain further information about superstable theories. In particular, his work is aimed at extending Shelah's classification results to uncountable theories. This should result in new structural information regarding the models of superstable theories, countable or not. In addition, Chowdhury plans to examine which properties of superstable theories can be generalised to a broader class, called supersimple theories. Supersimple theories, though not necessarily stable, exhibit some of the important characteristics of superstable theories. In model theory one studies those mathematical objects (called 'models") which satisfy a given collection of axioms. While one may think of a group as the set of transformations , or symmetries, of a particular object - such as an organic molecule, the general class of objects known as groups are precisely the models of the three group axioms. In algebra, one attempts to understand complicated objects (e.g., groups) in terms of how they are built from well-understood objects; when this succeeds, this is called a "structure theory". In model theory, one considers a general set of axioms and the collection of models, and asks whether there are properties inherent in the set of axioms which guarantee the existence of a structure theory. Rather remarkably, it turns out that certain abstract properties of a set of axioms do indeed imply certain structural features for the corresponding objects; one such property is called "superstability". The principal investigator proposes to continue the study of superstability (and its variations) and of its structural implications for a broader array of objects, one which includes interesting and important mathematical classes.