Existence and Density of General Components of the Noether–Lefschetz Locus on Normal Threefolds
Existence and Density of General Components of the Noether–Lefschetz Locus on Normal Threefolds
Abstract We consider the Noether–Lefschetz problem for surfaces in ${\mathbb Q}$-factorial normal 3-folds with rational singularities. We show the existence of components of the Noether–Lefschetz locus of maximal codimension, and that there are indeed infinitely many of them. Moreover, we show that their union is dense in the natural topology.