Pointed Evaluation Fibers of Rational Curves on del Pezzo Manifolds

Abstract

Let $X$ be a Picard-rank-one del Pezzo manifold of dimension $n\ge 4$ over an algebraically closed field of characteristic zero. Okamura proved that the unpointed Kontsevich spaces ${\overline{M}}_{0,0}(X,d)$ are irreducible of the expected dimension for every $d\ge 1$. We refine this result by studying pointed evaluation fibers. First, we prove that for every $d\ge 1$, the one-pointed evaluation morphism ${\overline{M}}_{0,1}(X,d)\to X$ has geometrically irreducible generic fiber. Second, in the very ample cases $H^n=3,4,5$, we prove that for every $d\ge 2$, the two-pointed evaluation morphism ${\overline{M}}_{0,2}(X,d)\to X\times X$ has geometrically irreducible generic fiber.