Rahul Ajit

Counterexamples to the Ambro--Kawamata effective non-vanishing conjecture

Let $k$ be an algebraically closed field of characteristic $0$ or $p\neq3$. We construct a terminal projective 4-fold $X$ and an ample Cartier divisor $D$ such that \[ 3K_X\sim0,\qquad D-K_X\ \text{is ample},\qquad H^0(X,D)=0. \] In char 0, this disproves Ambro--Kawamata effective non-vanishing conjecture. From this ex...