buondì,

vi segnalo il seminario di geometria di oggi, alle 16 come sempre, ma in aula magna. a presto, Bruno

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15-Jul-2015 - 16:00 Aula Magna (Dip. Matematica) Marco Castronovo

Twisted Whitney towers and concordance of links

Abstract: The Whitney trick can be used to remove intersection points in generic immersed concordances of links. Due to the fact that Whitney disks may intersect the concordance and each other, sometimes one only trades old with new intersections and these organize in "towers" that admit a combinatorial description in terms of trees modulo some relations. These relations show up in other areas of topology like those of quantum and finite type invariants. For example, there is a connection with Milnor invariants and the Kontsevich integral. Some subtelties regarding framing of Whitney disks suggest that a "twisted" version of these towers should be related to new concordance invariants with values in powers of Z/2 generalizing the classical Arf invariant of knots.