Lower and Upper Bounds for Nef Cones

The nef cone of a projective variety Y is an important and often elusive invariant. In this paper, we construct two polyhedral lower bounds and one polyhedral upper bound for the nef cone of Y using an embedding of Y into a toric variety. The lower bounds generalize the combinatorial description of the nef cone of a Mori dream space, while the upper bound generalizes the F-conjecture for the nef cone of the moduli space (M) Over bar(0,pi) to a wide class of varieties.