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Department of Mathematics,
Department of Mathematics,
University of California San Diego
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Math 209 - Number Theory Seminar
Gabriel Dorfsman-Hopkins
UC Berkeley
Untilting Line Bundles on Perfectoid Spaces
Abstract:
Let $X$ be a perfectoid space with tilt $X^\flat$. We build a natural map $\theta:\mathrm{Pic} X^\flat\to\lim\mathrm{Pic} X$ where the (inverse) limit is taken over the $p$-power map, and show that $\theta$ is an isomorphism if $R = \Gamma(X,\mathcal{O}_X)$ is a perfectoid ring. As a consequence we obtain a characterization of when the Picard groups of $X$ and $X^\flat$ agree in terms of the $p$-divisibility of $\mathrm{Pic} X$. The main technical ingredient is the vanishing of higher derived limits of the unit group $R^*$, whence the main result follows from the Grothendieck spectral sequence.
November 18, 2021
1:00 PM
APM 6402 and Zoom; see https://www.math.ucsd.edu/$\sim$nts/
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