A notion of delta-multigenus for certain rank two ample vector bundles

Abstract

A notion of "delta-genus" for ample vector bundles g of rank two on a smooth projective threefold X is defined as a couple of integers (delta(1),delta(2)).This extends the classical definition holding for ample line bundles. Then pairs (X, epsilon) with low delta(1) and delta(2) are classified under suitable additional assumptions on epsilon.