The Tate Intermediate Value Theorem
Paul Balmer, Beren Sanders
TL;DR
The Tate Intermediate Value Theorem provides a precise mechanism for gluing the open and closed pieces of a tensor-triangular spectrum along the support of a Tate ring. By constructing completions along a Thomason subset $Y$ and analyzing the induced spectral map $\varphi:\mathrm{Spc}(\hat{\mathscr{T}}^{\mathrm{d}})\to \mathrm{Spc}(\mathscr{T}^{\mathrm{d}})$, the authors show that specialization relations across $Y$ are controlled by the Tate ring's support $\mathrm{Supp}(\mathbb{t}_Y)$ and the image of completion. The main result states that $x\leadsto y$ with $x\notin Y$, $y\in Y$ holds iff there exists $z$ in $\mathrm{Supp}(\mathbb{t}_Y)$ with $x\leadsto z\leadsto y$, and they prove a strong version giving an intermediate specialization in the completion that maps between the two sides. This Tate IVT yields a pushout description of $\mathrm{Spc}(\mathscr{T}^{\mathrm{d}})$ as the amalgam of the open piece $\mathrm{Spc}(\mathscr{T}|_{U}^{\mathrm{d}})$ and the completion $\mathrm{Spc}(\hat{\mathscr{T}}^{\mathrm{d}})$ glued along the completion of the intersection, aligning with fracture-square perspectives in modern homotopy theory. The paper also develops extensive functoriality, excision, and localization machinery and provides rich examples spanning chromatic, equivariant, and modular representation theory, illustrating the general gluing principle in concrete settings.
Abstract
We explain how the gluing of a closed piece of the tensor-triangular spectrum with its open complement hinges on the support of the Tate ring.
