Poincaré polynomials of moduli spaces of one-dimensional sheaves on the projective plane

Abstract

Let $M_{\beta }$ denote the moduli space of stable one-dimensional sheaves on a del Pezzo surface $S$, supported on curves of class $\beta$ with Euler characteristic one. We show that the divisibility property of the Poincaré polynomial of $M_{\beta }$, proposed by Choi-van Garrel-Katz-Takahashi follows from Bousseau's conjectural refined sheaves/Gromov-Witten correspondence. Since this correspondence is known for $S={\mathbb{P}}^2$, our result proves Choi-van Garrel-Katz-Takahashi's conjecture in this case. For $S={\mathbb{P}}^2$, our proof also introduces a novel approach to computing the Poincaré polynomials using Gromov-Witten invariants of local ${\mathbb{P}}^2$ and a local elliptic curve. Specifically, we compute the Poincaré polynomials of $M_d$ with degrees $d\le 16$ and derive a closed formula for the leading Betti numbers $b_i(M_d)$ with $d\ge 6$ and $i\le 4d-22$. We also propose a conjectural formula for the leading Betti numbers $b_i(M_d)$ with $d\ge 4$ and $i\le 6d-20$. In the Appendix (by M. Moreira), a more general conjecture concerning the higher range Betti numbers of $M_d$ is presented, along with another conjecture that involves refinements from the perverse/Chern filtration.

We add an appendix by M. Moreira where a more general conjecture concerning the higher range Betti numbers of the moduli of one-dimensional sheaves on ${\mathbb{P}}^2$ is presented, along with another conjecture that involves refinements from the perverse/Chern filtration. Conjecture 1.9 has made more precise. 37 pages. Comments are welcome!