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.