The Riemann-Roch strategy, Complex lift of the Scaling Site

Abstract

We describe the Riemann-Roch strategy which consists of adapting in characteristic zero Weil's proof, of RH in positive characteristic, following the ideas of Mattuck, Tate and Grothendieck. As a new step in this strategy we implement the technique of tropical descent that allows one to deduce existence results in characteristic one from the Riemann-Roch result over the complex numbers. In order to deal with arbitrary distribution functions this technique involves the results of Bohr, Jessen and Tornehave on almost periodic functions. Our main result is the construction, at the adelic level, of a complex lift of the adele class space of the rationals. We interpret this lift as a moduli space of elliptic curves endowed with a triangular structure. The equivalence relation yielding the noncommutative structure is generated by isogenies. We describe the tight relation of this complex lift with the GL(2)-system. We construct the lift of the Frobenius correspondences using the Witt construction in characteristic one.