A converse to geometric Manin's conjecture for general low degree hypersurfaces and Poincaré duality

Abstract

Geometric Manin's conjecture predicts that components of the moduli space of curves on a Fano variety parametrizing non-free curves are pathological and arise from "accumulating" morphisms that increase the Fujita invariant. By passing to positive characteristic and employing a higher genus generalization of the circle method, we prove a converse to this conjecture for general hypersurfaces $X$ in ${\mathbb{P}}^n$ of degree $d\le n/4+3/2$, namely that there are no such accumulating maps to $X$. One consequence of this is a version of Poincaré duality for these moduli spaces in a range.

18 pages; fixed typos, improved exposition, and added an application