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Helicity is the only integral invariant of volume-preserving transformations
Alberto Enciso1, Daniel Peralta-Salas1, Francisco Torres de Lizaur1
1Instituto de Ciencias Matemáticas, Consejo Superior de Investigaciones Científicas, 28049 Madrid, Spain aenciso@icmat.es dperalta@icmat.es fj.torres@icmat.es.
Abstract:
We prove that any regular integral invariant of volume-preserving transformations is equivalent to the helicity. Specifically, given a functional I defined on exact divergence-free vector fields of class C(1) on a compact 3-manifold that is associated with a well-behaved integral kernel, we prove that I is invariant under arbitrary volume-preserving diffeomorphisms if and only if it is a function of the helicity.
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