# Geometry and Topology Seminar, 1 NOV, Gregory Arone. Title “Tree complexes and obstructions to embeddings.”

Department of Mathematics                                                           University of  Haifa

Geometry & Topology Seminar

Speaker:  Gregory Arone (Stockholm University)

Topic:  Tree complexes and obstructions to embeddings.

Place:    room 614 in the Science & Education Building

Time   12:10

Date:  Thursday, November 1, 2018

Abstract:

Abstract: Using the framework of the calculus of functors (a combination of manifold and orthogonal calculus) we define a sequence of obstructions for embedding a smooth manifold (or more generally a CW complex) M in R^d. The first in the sequence is essentially Haefliger’s obstruction (or van Kampen obstruction in the case of CW complexes). The second one was studied by Brian Munson. We interpret the n-th obstruction as a cohomology of configurations of n points on M with coefficients in the homology of a complex of trees with n leaves. The latter can be identified with the cyclic Lie_n representation. We will illustrate the theory with some examples involving embedding 2-dimensional complexes in R^4. The part having to do with CW complexes, especially embedding 2-complexes in R^4, is joint with Slava Krushkal. All of this is very much work in progress.

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