Arithmetic of Abelian Varieties - Complex Multiplication

Complex Multiplication

Since the time of Gauss (who knew of the lemniscate function case) the special role has been known of the A with extra automorphisms, and more generally endomorphisms. In terms of the ring End(A) there is a definition of abelian variety of CM-type that singles out the richest class. These are special in their arithmetic. This is seen in their L-functions in rather favourable terms – the harmonic analysis required is all of the Pontryagin duality type, rather than needing more general automorphic representations. That reflects a good understanding of their Tate modules as Galois modules. It also makes them harder to deal with in terms of the conjectural algebraic geometry (Hodge conjecture and Tate conjecture). In those problems the special situation is more demanding than the general.

In the case of elliptic curves, the Kronecker Jugendtraum was the programme Kronecker proposed, to use elliptic curves of CM-type to do class field theory explicitly for imaginary quadratic fields – in the way that roots of unity allow one to do this for the field of rational numbers. This generalises, but in some sense with loss of explicit information (as is typical of several complex variables).