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EXTENSIONS OF VECTOR BUNDLES ON THE FARGUES-FONTAINE CURVE

Published online by Cambridge University Press:  14 May 2020

Christopher Birkbeck
Affiliation:
Department of Mathematics, University College London, Gower street, WC1E 6BT ([email protected])
Tony Feng
Affiliation:
MIT Department of Mathematics, 182 Memorial Dr., Cambridge, MA02142 ([email protected])
David Hansen
Affiliation:
Max Planck Institute for Mathematics, Vivatsgasse 7, 53111Bonn, Germany ([email protected])
Serin Hong
Affiliation:
Department of Mathematics, University of Michigan, 530 Church Street, Ann Arbor, MI48109, USA ([email protected])
Qirui Li
Affiliation:
Department of Mathematics, Columbia University, 2990 Broadway, New York, 10 NY10027, USA ([email protected])
Anthony Wang
Affiliation:
Department of Mathematics, University of Chicago, 5734 S. University Avenue, Chicago, IL60637, USA ([email protected])
Lynnelle Ye
Affiliation:
Department of Mathematics, Building 380, Stanford, California 94305 ([email protected])

Abstract

We completely classify the possible extensions between semistable vector bundles on the Fargues–Fontaine curve (over an algebraically closed perfectoid field), in terms of a simple condition on Harder–Narasimhan (HN) polygons. Our arguments rely on a careful study of various moduli spaces of bundle maps, which we define and analyze using Scholze’s language of diamonds. This analysis reduces our main results to a somewhat involved combinatorial problem, which we then solve via a reinterpretation in terms of the Euclidean geometry of HN polygons.

MSC classification

Type
Research Article
Copyright
© The Author(s) 2020. Published by Cambridge University Press

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Footnotes

DH is grateful to Christian Johansson for some useful conversations about the material in § 3.2, and Peter Scholze for providing early access to the manuscript [13] and for some helpful conversations about the results therein. The project group students (CB, TF, SH, QL, AW, and LY) thank DH and Kiran Kedlaya for suggesting the problem. TF gratefully acknowledges the support of an NSF Graduate Fellowship. LY gratefully acknowledges the support of the National Defense Science and Engineering Graduate Fellowship. We would also like to thank David Linus Hamann and the referee for their valuable feedback on the first version of this paper.

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