Penn Arts & Sciences Logo

Penn Mathematics Colloquium

Wednesday, December 8, 2021 - 3:45pm

Kirsten Wickelgren

Duke University

Location

University of Pennsylvania

A4 DRL

Tea at 3:15pm in 4E17 DRL.

There is a unique line through 2 points in the plane, and a unique conic through 5. These counts generalize to a count of degree d rational curves in the plane passing through 3d-1 points.  Surprisingly, the problem of determining these numbers is connected to string theory, and it was not until the 1990's that Kontsevich determined them with a recursive formula. Such formulas are valid when you allow your curves to be defined with complex coefficients. Over the real numbers, one can obtain a fixed number by weighting real rational curves by their Welschinger invariant, and work of Solomon provides a recursive formula. It is a feature of A1-homotopy theory that analogous real and complex results can indicate the presence of a common generalization, valid over a general field. For fields of characteristic not 2 or 3, we give such a generalization. The resulting count is (the stable isomorphism class) of a bilinear form, or an element of the group completion GW(k) of symmetric, non-degenerate, bilinear forms over k. For example, there are 2(<1>+<-1>) + 6<1> + <2>+<2D> rational degree 3-plane curves passing through a general configuration of 6 k-points and a pair of conjugate k(sort{D}) points in the plane. No knowledge of A1-homoltopy theory or GW is assumed. This is joint work with Jesse Kass, Marc Levine, and Jake Solomon.

 

Other Events on This Day

There are no other events scheduled for this day.