Dual F-signature of Cohen-Macaulay modules over rational double points

Abstract

The dual $F$-signature is a numerical invariant defined via the Frobenius morphism in positive characteristic. It is known that the dual $F$-signature characterizes some singularities. However, the value of the dual $F$-signature is not known except only a few cases. In this paper, we determine the dual $F$-signature of Cohen-Macaulay modules over two-dimensional rational double points. The method for determining the dual $F$-signature is also valid for determining the Hilbert-Kunz multiplicity. We discuss it in appendix.