Aspects of Iwasawa theory over function fields

Abstract

We consider $\mathbb Z_p^{\mathbb{N}}$-extensions $\mathcal F$ of a global function field $F$ and study various aspects of Iwasawa theory with emphasis on the two main themes already (and still) developed in the number fields case as well. When dealing with the Selmer group of an abelian variety $A$ defined over $F$, we provide all the ingredients to formulate an Iwasawa Main Conjecture relating the Fitting ideal and the $p$-adic $L$-function associated to $A$ and $\mathcal F$. We do the same, with characteristic ideals and $p$-adic $L$-functions, in the case of class groups (using known results on characteristic ideals and Stickelberger elements for $\mathbb Z_p^d$-extensions). The final section provides more details for the cyclotomic $\mathbb Z_p^{\mathbb{N}}$-extension arising from the torsion of the Carlitz module: in particular, we relate cyclotomic units with Bernoulli–Carlitz numbers by a Coates–Wiles homomorphism.