Fibers of phase tropicalizations

TL;DR

This paper develops a general theory of phase tropicalization, extending classical tropicalization to non-abelian groups, and applies it to the special linear group SL_2, providing new algebraic insights.

Contribution

It introduces valuative tools for non-abelian tropicalizations, proves an affine Kapranov's theorem, and explains phase tropicalization for SL_2 and curves.

Findings

Established functorial properties of the graded ring of a valuation.

Proved an affine version of Kapranov's theorem for tropical hypersurfaces.

Provided algebraic explanations for phase tropicalization of curves and SL_2.

Abstract

The subject of the present paper is phase tropicalization, which was used crucially in the context of Mikhalkin's correspondence theorem for curve counting in the complex coefficient case. The subject can be traced back to Viro's patchworking for constructing topological types of real algebraic curves. These two instances correspond to complex and real phases. Both fall into the category of what can be called "abelian" or classical tropicalization, referring to degenerations of varieties within an algebraic torus (or its compactification). In contrast, in "non-abelian" tropicalizations the ambient torus is replaced by a non-commutative group such as the special linear group. This is the beginning of a general theory valid for a wide array of coefficient systems and dimensions. As an application, the paper settles the question of phase tropicalization for the special linear group $\mathrm{SL}_2$. It also gives an algebraic explanation and phase extension of the case of curves, previously studied in the purely geometric framework. To accomplish these tasks we introduce valuative tools that allow us to prove an affine version of Kapranov's theorem on tropical hypersurfaces and its generalization to arbitrary tropical varieties. Most notably, we show the functorial properties of the graded ring of a valuation and exhibit the polynomial structure of the graded ring of monomial valuations.