A Weil–Barsotti formula for Drinfeld modules Original Research Article

We study the group of extensions in the category of Drinfeld modules and Andersonʹs t-modules, and we show in certain cases that this group can itself be given the structure of a t-module. Our main result is a Drinfeld module analogue of the Weil–Barsotti formula for abelian varieties. Extensions of general t-modules are also considered, in particular extensions of tensor powers of the Carlitz module. We motivate these results from various directions and compare to the situation of elliptic curves.