On the Picard number of almost Fano threefolds with pseudo-index >1
C. Casagrande, P. Jahnke, I. Radloff
Abstract
We study Gorenstein almost Fano threefolds X with canonical singularities and pseudoindex > 1. We show that the maximal Picard number of X is 10 in general, 3 if X is Fano, and 8 if X is toric. Moreover, we characterize the boundary cases. In the Fano case, we prove that the generalized Mukai conjecture holds.
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