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Christian Dahlhausen

Publications and source records attributed to Christian Dahlhausen.

8 recordsLinked to original sources
arXiv2026

Representability of continuous K-theory in rigid analytic motivic $\mathbb{A}^1$-homotopy theory

We prove that both continuous K-theory and analytic K-theory of rigid analytic spaces (à la Kerz--Saito--Tamme) satisfiy descent with respect to the Nisnevich topology. Together with the fact that it is $\mathbb{A}^1$-invariant assuming resolutions of singularities, we deduce that it is representable in the $\mathbb{A}^{1}$-homotopy category of rigid spaces (à la Dahlhausen--Yaylali). We identifiy the representing object with both $\mathbb{Z}\times\mathrm{BGL}$ and the analytification of algebraic K-theory. As a consequence, we get a representability statement for coefficients in light condensed spectra. Moreover, we show Weibel vanishing and that continuous K-theory is $\mathbb{A}^1$-invariant on local Tate pairs (without any regularity assumption).

math.KT↗
arXiv2026

Towards $\mathbb{A}^1$-homotopy theory of rigid analytic spaces

To any rigid analytic space (in the sense of Fujiwara--Kato) we assign an $\mathbb{A}^1$-invariant rigid analytic homotopy category with coefficients in any presentable category. We show some functorial properties of this assignment as a functor on the category of rigid analytic spaces. Moreover, we show that there exists a full six-functor formalism for the precomposition with the analytification functor by evoking Ayoub's thesis. As an application, we prove mod $p$ rigidity for rigid spaces over $\mathbb{Q}_p$. Moreover, we prove the equivalence of $\mathbb{A}^1$-invariant sheaves and $\mathbb{B}^1$-invariant sheaves in the mod $\ell$ case.

math.AT↗
arXiv2025

Motivic homotopy theory for perfect schemes

We construct a perfect version of Morel--Voevodsky's motivic homotopy category over a perfect base scheme in positive characteristic. By checking the axioms of a coefficient system, we establish a six-functor formalism. We show that multiplication by $p$ is already invertible in the perfect motivic homotopy catgory. By work of Elmanto--Khan the functor sending an $\mathbb{F}_p$-scheme $S$ to the category $\mathrm{S}\mathcal{H}(S)[1/p]$ is invariant under universal homeomorphisms, hence under perfections. Our result gives an explicit model for the localization of $\mathrm{S}\mathcal{H}$ at the universal homeomorphisms, which we conclude is the same as $\mathrm{S}\mathcal{H}[1/p]$.

math.AG↗
arXiv2025

Regularity of semi-valuation rings and homotopy invariance of algebraic K-theory

We show that the algebraic K-theory of semi-valuation rings with stably coherent regular semi-fraction ring satisfies homotopy invariance. Moreover, we show that these rings are regular if their valuation is non-trivial. Thus they yield examples of regular rings which are not homotopy invariant for algebraic K-theory. On the other hand, they are not necessarily coherent, so that they provide a class of possibly non-coherent examples for homotopy invariance of algebraic K-theory. As an application, we show that Temkin's relative Riemann-Zariski spaces also satisfy homotopy invariance for K-theory under some finiteness assumption.

math.KT↗
arXiv2024

Continuous K-Theory and Cohomology of Rigid Spaces

We establish a connection between continuous K-theory and integral cohomology of rigid spaces. Given a rigid analytic space over a complete discretely valued field, its continuous K-groups vanish in degrees below the negative of the dimension. Likewise, the cohomology groups vanish in degrees above the dimension. The main result provides the existence of an isomorphism between the lowest possibly non-vanishing continuous K-group and the highest possibly non-vanishing cohomology group with integral coefficients. A key role in the proof is played by a comparison between cohomology groups of an admissible Zariski-Riemann space with respect to different topologies; namely, the rh-topology which is related to K-theory as well as the Zariski topology whereon the cohomology groups in question rely.

math.KT↗
arXiv2024

K-theory of admissible Zariski-Riemann spaces

We study relative algebraic K-theory of admissible Zariski-Riemann spaces and prove that it is equivalent to G-theory and satisfies homotopy invariance. Moreover, we provide an example of a non-noetherian abelian category whose negative K-theory vanishes.

math.KT↗
arXiv2017

Milnor K-theory of complete discrete valuation rings with finite residue fields

Consider a complete discrete valuation ring $\mathcal{O}$ with quotient field $F$ and finite residue field. Then the inclusion map $\mathcal{O} \hookrightarrow F$ induces a map $\hat{\mathrm{K}}^\mathrm{M}_*\mathcal{O} \to \hat{\mathrm{K}}^\mathrm{M}_*F$ on improved Milnor K-theory. We show that this map is an isomorphism in degrees bigger or equal to 3. This implies the Gersten conjecture for improved Milnor K-theory. This result is new in the $p$-adic case.

math.KT↗