A mirror theorem for Gromov-Witten theory without convexity

Abstract We prove a genus zero Givental-style mirror theorem for all complete intersections in toric Deligne-Mumford stacks, which provides an explicit slice called big I -function on Givental’s Lagrangian cone for such targets. In particular, we remove a technical assumption called convexity needed in the previous mirror theorem for such complete intersections. In the realm of quasimap theory, our mirror theorem can be viewed as solving the quasimap wall-crossing conjecture for big I -function [13] for these targets. In the proof, we discover a new recursive characterization of the slice on Givental’s Lagrangian cone, which may be of self-independent interests.