Knots in Contact Geometry

Dmitry Fuchs, University of California at Davis

Abstract. Legendrian knots in the standard contact space are smooth knots in space tangent to the plane distribution determined by the form y dx - dz. There are classical Legendrian isotopy invariants of Legendrian knots, such as the Thurston-Bennequin and rotation numbers, and more modern invariants, such as contact homology.

A (generic) Legendrian knot is determined by its xz-projection (front diagram), which is a smooth closed curve in the plane with transverse self-intersections and cusps, but without vertical tangents and self-tangencies. In the early 2000's, a visualizable combinatorial structure on front diagrams was discovered; it is called a normal ruling. The existence of a normal ruling turns out to be necessary and sufficient for some seemingly unrelated properties of Legendrian knots, such as the existence of a generating family of functions and certain relations between the abovementioned invariants.

The talk will contain a survey of results of this kind with an emphasis on a recently discovered connection between the generating families and the contact homology. It will be elementary: everything needed beyond the standard undergraduate courses will be defined and explained.