Moishezon Spaces and Projectivity Criteria

Abstract

We show that a smooth Moishezon space $Y$ is non-projective if and only if it contains a rational curve such that $-[C] \in \overline{\mathrm{NE}}(Y)$. More generally, this holds if $Y$ has $\mathbb{Q}$-factorial, log terminal singularities. We derive this as a consequence of our main technical result: that we can run the relative minimal model program when the base is a normal algebraic space $Y$ of finite type over a field of characteristic $0$. As a second application, we show that every log canonical pair $(Y, \Delta)$, where $Y$ is an algebraic space of finite type over a field of characteristic $0$ admits a dlt modification that is projective over $Y$.