Effective non-vanishing conjectures for projective threefolds
Résumé
Let X be a smooth projective threefold, and let A be an ample line bundle such that K_X+A is nef. We show that if K_X or -K_X is pseudoeffective, the adjoint bundle K_X+A has global sections. We also give a very short proof of the Beltrametti-Sommese conjecture in dimension three, recently proven by Fukuma: if A is an ample line bundle such that K_X+2A is nef, the adjoint bundle K_X+2A has global sections.