A Generalization of Lifting Non-proper Tropical Intersections

TL;DR

This paper extends tropical intersection theory by proving rational equivalence between algebraic and tropical intersections, allowing for positive-dimensional intersections and compactifications, thus broadening the scope of tropical geometry applications.

Contribution

It generalizes the tropical intersection theory to include positive-dimensional intersections and introduces a compatible compactified stable intersection in toric tropical varieties.

Findings

Proves rational equivalence between algebraic and tropical intersections.

Defines a compatible compactified stable intersection in toric tropical varieties.

Generalizes previous work to intersections of positive dimension.

Abstract

Let X and X' be closed subschemes of an algebraic torus T over a non-archimedean field. We prove the rational equivalence as tropical cycles, in the sense of Henning Meyer's graduate thesis, between the tropicalization of the intersection product of X and X' and the stable intersection of trop(X) and trop(X'), when restricted to (the inverse image under the tropicalization map of) a connected component C of the intersection of trop(X) and trop(X'). This requires possibly passing to a (partial) compactification of T with respect to a suitable fan. We define the compactified stable intersection in a toric tropical variety, and check that this definition is compatible with the intersection product in loc.cit.. As a result we get a numerical equivalence (after a compactification and restricting to C) between the intersection product of X and X' and the stable intersection of trop(X) and trop(X') via the compactified stable intersection. In particular, when X and X' have complementary codimensions, this equivalence generalizes the work of Osserman and Rabinoff, in the sense that the intersection of X and X' is allowed to be of positive dimension. Moreover, if the intersection of the closures of X and X' has finitely many points which tropicalize to the closure of C, we prove a similar equation as in Theorem 6.4 of the paper of Osserman and Rabinoff when the ambient space is a reduced closed subscheme of T (instead of T itself).