A1-enumerative geometry
It is a feature of A1-homotopy theory that analogous results over the complex and real numbers may indicate the presence of a common generalization valid over a general field k. For example, there are 15⟨1⟩+12⟨−1⟩ lines on a cubic surface, and ⟨1⟩+⟨−1⟩ lines through four lines in space. The counts now take values in the Grothendieck-Witt group of stable isomorphism classes of non-degenerate, symmetric bilinear forms. ⟨a⟩ represents the class of the bilinear form k×k↦k mapping (x,y) to axy. The above examples are from joint work with Jesse Kass and Padma Srinivasan. Results over R and C can be recovered by taking the rank and the signature. This talk will introduce A1-enumerative geometry and present a wall-crossing formula for A1 Gromov-Witten invariants joint with Erwan Brugallé.