The convergent stack

Abstract

Inspired by Simpson's de Rham stack and Drinfeld's crystalline stack, we develop a stacky approach to convergent cohomology and convergent isocrystals in positive characteristic. To any scheme $X$ over ${\mathbb{F}}_p$ we attach a convergent stack $X_{\mathrm{conv}}$. When $X$ is of finite type over a perfect field, its finitely generated quasi-coherent $\mathcal{O}[\frac{1}{p}]$-modules are equivalent to convergent isocrystals over $X$, compatibly with cohomology. When $X$ embeds into a smooth $p$-adic formal scheme, we describe $X_{\mathrm{conv}}$ explicitly as the quotient of an open tube by a $p$-adic formal groupoid. For $f$-semiperfect schemes, by contrast, the convergent stack is representable by a preperfectoid adic space over ${\mathbb{Q}}_p$.

19 pages