Non-elementary Fano conic bundles (1605.07590v2)

Abstract: We study a particular kind of fiber type contractions between complex, projective, smooth varieties f:X->Y, called Fano conic bundles. This means that X is a Fano variety, and every fiber of f is isomorphic to a plane conic. Denoting by rho_{X} the Picard number of X, we investigate such contractions when rho_{X}-rho_{Y} is greater than 1, called non-elementary. We prove that rho_{X}-rho_{Y} is at most 8, and we deduce new geometric information about our varieties, depending on rho_{X}-rho_{Y}. Moreover, when X is locally factorial with canonical singularities and with at most finitely many non-terminal points, we consider fiber type K_{X}-negative contractions f:X->Y with one-dimensional fibers, and we show that rho_{X}-rho_{Y} is at most 9.