Filtered Geometric Lattices and Lefschetz Section Theorems Over the Tropical Semiring
FILTERED GEOMETRIC LATTICES AND LEFSCHETZ SECTION THEOREMS OVER THE TROPICAL SEMIRING KARIM ADIPRASITO AND ANDERS BJÖRNER ABSTRACT. The purpose of this paper is to establish analogues of the classical Lefschetz Sec- tion Theorem for smooth tropical varieties. We attempt to give a comprehensive picture of the Lefschetz Section Theorem in tropical geometry by deriving tropical analogues of many of the classical Lefschetz theorems and associated vanishing theorems. We start the paper by resolving a conjecture of Mikhalkin and Ziegler (2008) concerning the homotopy type of certain filtrations of geometric lattices, generalizing several known properties of full geometric lattices. This translates to a crucial index estimate for the stratified Morse data at critical points of the tropical variety. The tropical varieties that we deal with are locally matroidal, and the Lefschetz theorems are shown to apply also in the case of nonrealizable matroids. Tropical geometry is a relatively young field of mathematics, based on early work of, among many others, Bergman [Ber71] and Bieri–Groves [BG84]. It arises as algebraic geometry over the tropical max-plus semiring T = ([−∞, ∞), max, +), and also as a limit of classical complex algebraic geometry. Since tropical varieties are, in essence, polyhedral spaces, tropical geom- etry naturally connects the fields of algebraic and combinatorial geometry, and combinatorial tools have proven essential for the study of tropical varieties. Since its origins, tropical geometry has been extensively developed [Gat06, RGST05, Spe05, SS09]. It has been applied to classical algebraic geometry [Gub07], enumerative algebraic geometry [KT02, Mik05, Mik06, Shu05], mirror symmetry [Gro11, KS01], integrable systems [AMS12], and to several branches of applied mathematics, cf.
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