arXiv subjects

Ferdinand Wagner

Publications and source records attributed to Ferdinand Wagner.

5 recordsLinked to original sources

arXiv2025

$q$-Hodge complexes and refined $\operatorname{TC}^-$

As a consequence of Efimov's proof of rigidity of the $\infty$-category of localising motives, Efimov and Scholze have constructed refinements of localising invariants such as $\operatorname{THH}$ and $\operatorname{TC}^-$. These refinements often contain vastly more information than the original invariant. In this article we explain a general recipe how to compute the refinements in certain situations. We then apply this recipe to compute the homotopy groups of $\operatorname{TC}^{-,\mathrm{ref}}(\mathrm{ku}\otimes\mathbb Q/\mathrm{ku})$ and $\operatorname{TC}^{-,\mathrm{ref}}(\mathrm{KU}\otimes\mathbb Q/\mathrm{KU})$. The result has a rather surprising geometric description and contains non-trivial information modulo any prime, in contrast to the unrefined $\operatorname{TC}^-$.

math.AT↗

arXiv2025

$q$-Hodge complexes over the Habiro ring

Peter Scholze has raised the question whether some variant of the $q$-de Rham complex is already defined over the Habiro ring $\mathcal H = \lim_{m\in\mathbb N}\mathbb Z[q]_{(q^m-1)}^\wedge$. We show that such a variant exists whenever the $q$-de Rham complex can be equipped with a "$q$-Hodge filtration": a $q$-deformation of the Hodge filtration, subject to some reasonable conditions. To any such $q$-Hodge filtration we associate a small modification of the $q$-de Rham complex, which we call the $q$-Hodge complex, and show that it descends canonically to the Habiro ring. This construction recovers and generalises the Habiro ring of a number field of Garoufalidis-Scholze-Wheeler-Zagier and is closely related to the $q$-de Rham--Witt complexes from previous work of the author as well as, conjecturally, to Scholze's analytic Habiro stack. While there's no canonical $q$-Hodge filtration in general, we show that it does exist in many cases of interest. For example, for a smooth scheme $X$ over $\mathbb Z$, the $q$-de Rham complex can be equipped with a canonical $q$-Hodge filtration as soon as one inverts all primes $p\leq \dim(X/\mathbb Z)$.

math.AG↗

arXiv2025

$q$-de Rham cohomology and topological Hochschild homology over ku

Hodge-filtered derived de Rham cohomology of a ring $R$ can be described (up to completion and shift) as the graded pieces of the even filtration on $\mathrm{HC}^-(R)$. In this paper we show a deformation of this result: If $R$ admits a spherical $\mathbb{E}_2$-lift, then the graded pieces of the even filtration on $\mathrm{TC}^-(\mathrm{ku}\otimes\mathbb{S}_R/\mathrm{ku})$ form a certain filtration on the $q$-de Rham cohomology of $R$, which $q$-deforms the Hodge filtration. We also explain how the associated Habiro-Hodge complex can be described in terms of the genuine equivariant structure on $\mathrm{THH}(\mathrm{KU}\otimes\mathbb{S}_R/\mathrm{KU})$. As a special case, we'll obtain homotopy-theoretic construction of the Habiro ring of a number field of Garoufalidis-Scholze-Wheeler-Zagier.

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arXiv2025

$q$-Witt vectors and $q$-Hodge complexes

In this article, we'll introduce a $q$-variant of Witt vectors and de Rham-Witt complexes. This variant is closely related to the Habiro ring of a number field constructed by Garoufalidis, Scholze, Wheeler, and Zagier, to $q$-Hodge cohomology, and to $\operatorname{THH}(-/\mathrm{ku})$. While most of these connections will only be explored in forthcoming work, the goal of this article is to provide the necessary technical foundation.

math.NT↗

arXiv2023

Totally odd depth-graded multiple zeta values and period polynomials

Inspired by a paper of Tasaka, we study the relations between totally odd, motivic depth-graded multiple zeta values. Our main objective is to determine the rank of the matrix $C_{N,r}$ defined by Brown. We will give new proofs for (conjecturally optimal) upper bounds on the rank of $C_{N,3}$ and $C_{N,4}$, which were first obtained by Tasaka. Finally, we present a recursive approach to the general problem, which reduces evaluating the rank of $C_{N,r}$ to an isomorphism conjecture.

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