Geometric class field theory with bounded ramification

Abstract

Let U be a smooth quasi-projective variety over a field k that is finite, the algebraic closure of a finite field or algebraically closed of characteristic 0. Let X be a suitable projective compactification of U, and D an effective divisor on X with support in X\U. We consider a relative Chow group of modulus D, the Albanese variety of X of modulus D and the Abel-Jacobi map with modulus. We show that there is a 1-1 correspondence between relative Cartier divisors on X and compatible systems of relative Cartier divisors on curves in X. This allows us to prove a Roitman theorem with modulus, and we obtain a reciprocity law and an existence theorem for abelian coverings of X with ramification bounded by D. Changes to the previous version: X is of arbitrary dimension and not necessarily smooth, char(k) = 0 is included for the so called Skeleton Theorem and the Roitman Theorems, log as well as non-log versions are treated. The definition of the Chow group with modulus was inconsistent for singular curves, this is clarified now.