Motivic quasimap wall-crossing for Grassmannians

Abstract

We prove a wall-crossing formula for the Euler characteristics, considered as virtual mixed Hodge structures, of moduli spaces of $\varepsilon$-stable quasimaps to the Grassmannian $\mathbb{G}(r, N)$. For each $\varepsilon > 0$, we define a $\mathbb{Q}$-algebra automorphism of the ring of symmetric functions which takes the generating function for the $\mathbb{S}_n$-equivariant Euler characteristics of the moduli spaces of stable maps $\overline{\mathcal{M}}_{g, n}(\mathbb{G}(r, N), d)$ to the corresponding generating function for Toda's moduli spaces of $\varepsilon$-stable quasimaps $\overline{\mathcal{Q}}_{g, n}^{\varepsilon}(\mathbb{G}(r, N), d)$. The automorphism is given by explicit $q$-deformations of the power sum symmetric functions. The $\varepsilon \to 0$ limit of our formula exchanges the spaces of stable maps and the Marian--Oprea--Pandharipande moduli spaces of stable quotients. Our proof uses the geometry of relative Quot schemes to relate the quasimap spaces to moduli spaces of weighted stable maps, for which we obtain wall-crossing formulas via symmetric function theory.