### Helicity in differential topology

Mitsumatsu, Y *(Chuo University)*

Wednesday 25 July 2012, 10:10-10:30

Seminar Room 1, Newton Institute

#### Abstract

The helicity plays many intresting roles in 3-dimensinal diffential topology. One of its earliest appearences in was the question by Dennis Sullivan, asking to express the Godbilon-Vey invariant in terms of linking of fluids. Here the Godbillon-Vey is an invariant for codimension1 foliations which lives in the 3rd de Rham cohomology. The question is well-understood and we know which fluid motion should be taken.
If we think of helicity as a quadratic function on the space of incompressible fluids, namely the space of divergence free vector fields, it goes down to a symmetric bilinear form. Some ideas concerning this bilinear form for studies of foliations and contact structures are introduced. For example, in the case of codimmension one foliations the 1st foliated cohomology will appear. If the foliation is deofrmed to contact structures, unexpectedly phenomena which might be related to a quatization procedure is found.

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