arXiv subjects

Klaus Mattis

Publications and source records attributed to Klaus Mattis.

8 recordsLinked to original sources

arXiv2025

Nilpotence of $\eta$ in \'etale motivic spectra

We show that every object of the stable \'etale motivic homotopy category over any scheme is $\eta$-complete. In some cases we show that in fact the fourth power of $\eta$ is null, whereas the third power of $\eta$ is always nonvanishing, similar to the situation in topology. Moreover, we prove an \'etale version of May's nilpotence conjecture, that states that $H\mathbb{Z} \in \mathrm{Sp}$ detects the vanishing of $\mathbf{E}_\infty$-rings. We use this to show a version of Nishida's nilpotence theorem in $\mathrm{SH}_{\operatorname{\acute{e}t}}(S)$, i.e. that any positive degree self map of the unit is nilpotent.

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arXiv2025

Monadic resolutions for generalized spaces

We extend the work of Bousfield and Kan on monadic resolutions of spaces to $\infty$-topoi, with applications to genuine $G$-equivariant spaces ($G$ a finite group) and motivic spaces over a perfect field. In particular, we give a proof of the principal fibration lemma in this context. We apply the principal fibration lemma to prove convergence of several kinds of monadic resolutions in unstable equivariant and motivic homotopy theory. For example, we show that, over an algebraically closed field, the unstable Adams--Novikov spectral sequence (i.e., the monadic resolution corresponding to the algebraic cobordism spectrum $\mathrm{MGL}$) converges for all nilpotent, connected, $2$-effective motivic spaces.

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arXiv2025

The derived $\infty$-category of Frobenius modules

We prove that for $X$ a quasi-compact $\mathbb{F}_p$-scheme with affine diagonal (e.g.\ $X$ quasi-compact and separated) there is a t-exact equivalence $\mathcal D(\mathrm{Frob}(\mathrm{QCoh}(X),F_*)) \to \mathrm{Frob}(\mathcal D(\mathrm{QCoh}(X)),\mathcal D(F_*))$ of stable $\infty$-categories. Here, $\mathrm{Frob}(-,-)$ denotes the $\infty$-category of generalized Frobenius modules as introduced in arXiv:2410.17102. This generalizes our result from arXiv:2410.17102, where we proved the above for regular Noetherian $\mathbb{F}_p$-schemes. As a byproduct we prove that the derived $\infty$-category of Frobenius (and Cartier) modules satisfies Zariski descent.

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arXiv2025

Unstable \'etale motives

We prove a rigidity result for certain $p$-complete \'etale $\mathbf{A}^{1}$-invariant sheaves of anima over a qcqs finite-dimensional base scheme $S$ of bounded \'etale cohomological dimension with $p$ invertible on $S$. This generalizes results of Suslin--Voevodsky, Ayoub, Cisinski--D\'eglise, and Bachmann to the unstable setting. Over a perfect field we exhibit a large class of sheaves to which our main theorem applies, in particular the $p$-completion of the \'etale sheafification of any $2$-effective $2$-connective motivic space, as well as the $p$-completion of any $4$-connective $\mathbf{A}^{1}$-invariant \'etale sheaf. We use this rigidity result to prove (a weaker version of) an \'etale analog of Morel's theorem stating that for a Nisnevich sheaf of abelian groups, strong $\mathbf{A}^{1}$-invariance implies strict $\mathbf{A}^{1}$-invariance. Moreover, this allows us to construct an unstable \'etale realization functor on $2$-effective $2$-connective motivic spaces.

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arXiv2024

The derived $\infty$-category of Cartier Modules

For an endofunctor $F\colon\mathcal{C}\to\mathcal{C}$ on an ($\infty$-)category $\mathcal{C}$ we define the $\infty$-category $\operatorname{Cart}(\mathcal{C},F)$ of generalized Cartier modules as the lax equalizer of $F$ and the identity. This generalizes the notion of Cartier modules on $\mathbb{F}_p$-schemes considered in the literature. We show that in favorable cases $\operatorname{Cart}(\mathcal{C},F)$ is monadic over $\mathcal{C}$. If $\mathcal{A}$ is a Grothendieck abelian category and $F\colon\mathcal{A}\to\mathcal{A}$ is an exact and colimit-preserving endofunctor, we use this fact to construct an equivalence $\mathcal{D}(\operatorname{Cart}(\mathcal{A},F)) \simeq \operatorname{Cart}(\mathcal{D}(\mathcal{A}),\mathcal{D}(F))$ of stable $\infty$-categories. We use this equivalence to construct a perverse t-structure on $\mathcal{D}(\operatorname{Cart}(\operatorname{Mod}(X), F_*))$ for any Noetherian $\mathbb{F}_p$-scheme $X$ with absolute Frobenius $F$. If $F$ is finite, this coincides with the perverse t-structure constructed by Baudin.

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arXiv2024

Unstable arithmetic fracture squares in $\infty$-topoi

We show that for a large class of $\infty$-topoi there exist unstable arithmetic fracture squares, i.e. squares which recover a nilpotent sheaf $F$ as the pullback of the rationalization of $F$ with the product of the $p$-completions of $F$ ranging over all primes $p\in\mathbb Z$.

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arXiv2024

The pro-Nisnevich topology

We construct the pro-Nisnevich topology, an analog of the pro-étale topology. We then show that the Nisnevich $\infty$-topos embeds into the pro-Nisnevich $\infty$-topos, and that the pro-Nisnevich $\infty$-topos is locally of homotopy dimension $0$.

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arXiv2024

Unstable $p$-completion in motivic homotopy theory

We define unstable $p$-completion in general $\infty$-topoi and the unstable motivic homotopy category, and prove that the $p$-completion of a nilpotent sheaf or motivic space can be computed on its Postnikov tower. We then show that the ($p$-completed) homotopy groups of the $p$-completion of a nilpotent motivic space $X$ fit into short exact sequences $0 \to \mathbb L_0 π_n(X) \to π_n^p(X_p^\wedge) \to \mathbb L_1 π_{n-1}(X) \to 0$, where the $\mathbb L_i$ are (versions of) the derived $p$-completion functors, analogous to the classical situation.

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