Tame geometry and transcendence in Hodge theory

Hodge theory, as developed by Deligne and Griffiths, is the main tool for analyzing the geometry and arithmetic of complex algebraic varieties, that is, solution sets of algebraic equations over the complex numbers.

It occupies a central position in mathematics through its relations to differential geometry, algebraic geometry, differential equations and number theory. It is an essential fact that at heart, Hodge theory is NOT algebraic.

On the other hand, some of the deepest conjectures in mathematics (the Hodge conjecture and the Grothendieck period conjecture) suggest that this transcendence is severely constrained.Recent work of myself and others suggests that tame geometry, whose idea was introduced by Grothendieck in the 1980s, is the natural setting for understanding these constraints.

Tame geometry, developed by model-theorist as o-minimal geometry, has for prototype real semi-algebraic geometry, but is much richer.

As a spectacular application of tame geometry, Bakker, Tsimerman and I recently reproved a famous result of Cattani-Deligne-Kaplan, often considered as the most serious evidence for the Hodge conjecture: the algebraicity of Hodge loci.I propose to lead a group at HU Berlin to explore this striking new connection between tame geometry and Hodge theory, with three axes: (I) attack the arithmetic of periods coming from the moduli space of abelian differentials; this opens a completely new perspective on this space cherished by dynamicists; (II) attack some fundamental questions for general variations of Hodge structures: fields of definition of Hodge loci (related to the conjecture that Hodge classes are absolute Hodge classes); atypical intersections, for instance for families of Calabi- Yau varieties; Ax-Schanuel conjecture for mixed period maps and for Hodge bundles; (III) attack Simpsons Standard conjecture for local systems through the tame geometry of the non-abelian Hodge correspondence.