Bounds on the Picard rank of toric Fano varieties with minimal curve constraints

Abstract

We study the Picard rank of smooth toric Fano varieties possessing families of minimal rational curves of given degree. We discuss variants of a conjecture of Chen-Fu-Hwang and prove a version of their statement that recovers the original conjecture in sufficiently high dimension. We also prove new cases of the original conjecture for high degrees in all dimensions. Our main tools come from toric Mori theory and the combinatorics of Fano polytopes.

arXiv comment11 pages; v.2. thanks to Cinzia Casagrande for noticing an error that has been corrected with no changes to the results; v.3. minor typos fixed; v.4. final version; comments welcome!