Orientability in real Gromov-Witten theory

Abstract: The orientability problem in real Gromov-Witten theory is one of the fundamental hurdles to enumerating real curves. In this paper, we describe topological conditions on the target manifold which ensure that the uncompactified moduli spaces of real maps are orientable for all genera of and for all types of involutions on the domain. In contrast to the typical approaches to this problem, we do not compute the signs of any diffeomorphisms, but instead compare them. Many projective complete intersections, including the renowned quintic threefold, satisfy our topological conditions. Our main result yields real Gromov-Witten invariants of arbitrary genus for real symplectic manifolds that satisfy these conditions and have empty real locus and illustrates the significance of previously introduced moduli spaces of maps with crosscaps. We also apply it to study the orientability of the moduli spaces of real Hurwitz covers.