Seminar Calendar
for events the day of Thursday, November 19, 2009.

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Thursday, November 19, 2009

Mathematical and theoretical physics
11:30 am   in 464 Loomis or 322 Loomis,  Thursday, November 19, 2009
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Submitted by mando.
Prof. Aki Hashimoto (University of Wisconsin/Madison)
Branes and fluxes in manifolds of special holonomy and cascading field theories
Abstract: In this talk, I will motivate and describe some generalizations of ABJM construction, which can be viewed as decoupled theories of M2-branes in transverse eight dimensional manifolds of sp(2) holonomy, to cases involving holonomy groups spin(7) and sp(1)xsp(1). I will comment on the threshold of dynamical supersymmetry breaking in these models, and speculate on the features of the dual gravity description of the dynamically broken supersymmetry

Group Theory Seminar
1:00 pm   in Altgeld Hall 347,  Thursday, November 19, 2009
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Submitted by kapovitc.
Martin Evans (University of Alabama)
Relation Modules of Infinite Groups.
Abstract: Let A and B be relation modules of a d-generator group G, associated with presentations on $m\geq d$ generators, and let R denote the integral group ring of G. In general A and B are not isomorphic as R-modules although they are STABLY isomorphic. We discuss the minimal rank k such that the direct sum of A and the free R-module of rank k is isomorphic to the direct sum of B and the free R-module of rank k.

Number Theory Seminar
1:00 pm   in 241 Altgeld Hall,  Thursday, November 19, 2009
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Submitted by jarouse.
Andrew Shallue (Illinois Wesleyan)
Enumerating class group structures of real quadratic number fields
Abstract: There are many classic conjectures surrounding the structure of the ideal class group of real quadratic number fields. Among them are the Cohen-Lenstra heuristics, which give precise information about the expected structure of such class groups. Supporting such conjectures provides motivation to tabulate class numbers of quadratic number fields. I will discuss the present progress of a project to enumerate the structure of all class groups for discriminants of real quadratic number fields up to 10^11, and to do so without relying on the Extended Riemann Hypothesis. In essence, this has two main components. First, there are algorithms for computing the structure of an abelian group given group operations as a black box. Second, these group operations must be instantiated. This is nontrivial in the case of the ideal class group of a real quadratic number field. In addition to first computing the regulator, elements of the group do not have a unique representative, making identity testing a difficult proposition. We will see how these difficulties are overcome, and discuss exciting new developments in algorithms for finding the structure of a generic group.

Analysis Seminar
2:00 pm   in 243 Altgeld Hall,  Thursday, November 19, 2009
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Submitted by aimo.
Stephen Dilworth (University of South Carolina)
Convergence of some greedy algorithms in Banach spaces

Differential Geometry Seminar
3:00 pm   in 347 Altgeld Hall,  Thursday, November 19, 2009
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Submitted by clein.
Ken Bromberg (U. Utah)
The asymptotic dimension of the mapping class group
Abstract: We will show that the mapping class group has finite asymptotic dimension. A key piece of the proof is the construction of a quasi-tree that mapping class acts on. This construction works in a quite general setting for groups that have some aspect of negative curvature. We will describe this construction and explain how it relates to the asymptotic dimension of the mapping class group. This is joint work with K. Fujiwara and M. Bestvina.