# A chromatic approach to homological stability

## TL;DR

This paper introduces a chromatic perspective on higher-order homological stability, linking it to stable homotopy theory, Bousfield localisations, and Hopf algebra structures, providing new tools and results for understanding stability phenomena.

## Contribution

It develops a chromatic framework for higher-order homological stability, connecting it with Bousfield localisations, Smith--Toda complexes, and Hopf algebra invariants, offering new insights and methods.

## Key findings

- Established higher-order stability theorems with slopes tending to 1.
- Linked stable homology to Bousfield localisations and chromatic towers.
- Connected stability patterns to the cohomology of a Hopf algebra.

## Abstract

We propose a way to organise the subject of ``higher-order homological stability'', in the context of a graded $E_2$-algebra $\mathbf{R}$, along the same lines that the chromatic perspective organises stable homotopy theory. From this point of view proving a (higher-order) homological stability theorem corresponds to producing Smith--Toda complexes in the category of $\mathbf{R}$-modules: using this perspective we prove that whenever $\mathbf{R}$ is defined over a field of positive characteristic and satisfies some standard properties, there is a sequence of higher-order homological stability theorems whose slopes tend to 1. We propose that in a higher-order stable range the ``stable homology'' should be interpreted as certain Bousfield localisations in the category of $\mathbf{R}$-modules, leading to a chromatic tower and monochromatic layers. Given the existence of suitable Smith--Toda complexes we establish several properties of these localisations, in particular explaining how higher-order stabilisation maps yield periodic families in the monochromatic layers. We explain how to associate to such an $\mathbf{R}$ a Hopf algebra which completely governs the kinds of higher-order stability maps that it enjoys, in the sense that the cohomology of this Hopf algebra has precisely the same stability patterns as $\mathbf{R}$. When $\mathbf{R}$ comes from a sequence of groups, this Hopf algebra has a concrete description as the coinvariants of the $E_1$-Steinberg modules.

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Source: https://tomesphere.com/paper/2508.20629