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Igusa Stacks and the Langlands program

Objective

The Langlands program, often called a ``grand unified theory of mathematics'', predicts reciprocity laws that relate very different kinds of mathematical objects: automorphic forms and Galois representations. Shimura varieties play a fundamental role in constructing and propagating instances of Langlands reciprocity.

In the past decade, advances in p-adic geometry have revolutionised the study of Shimura varieties. This recently led to the introduction of certain p-adic analytic varieties called Igusa stacks, which connect Shimura varieties to ideas from geometric Langlands via the work of Fargues--Scholze. This gives access to powerful new tools and makes Igusa stacks seem as fundamental as the Shimura varieties themselves.

This proposal will realise the potential of p-adic Igusa stacks and of the closely related Igusa varieties to give a systematic understanding of the cohomology of Shimura varieties with l-torsion coefficients and of congruences modulo l between automorphic forms on Shimura varieties. There are two components to this proposal, depending on whether or not l = p.

When l is not p, I will construct the relative intersection cohomology of the Igusa stack and describe it in terms of purely local (generalised) eigensheaves, expanding on and proving a conjecture of Fargues. This will lead to a description of torsion in the intersection cohomology of Shimura varieties, reminiscent of Arthur's conjectures in characteristic 0, and to an axiomatic approach to congruences, such as level-raising, when the tame level varies.

When l is p, I will prove an integral Eichler--Shimura comparison theorem for ordinary p-adic automorphic forms. Initially, my approach will exploit the ordinary part of the Igusa stack, then move into deeper Newton strata for generalisations. This theorem will unify geometric and representation-theoretic perspectives on ordinary p-adic automorphic forms and will have major applications to Euler systems and Iwasawa theory.

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Topic(s)

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HORIZON-ERC - HORIZON ERC Grants

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Call for proposal

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(opens in new window) ERC-2025-COG

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Host institution

IMPERIAL COLLEGE OF SCIENCE TECHNOLOGY AND MEDICINE
Net EU contribution

Net EU financial contribution. The sum of money that the participant receives, deducted by the EU contribution to its linked third party. It considers the distribution of the EU financial contribution between direct beneficiaries of the project and other types of participants, like third-party participants.

€ 1 999 760,00
Address
SOUTH KENSINGTON CAMPUS EXHIBITION ROAD
SW7 2AZ London
United Kingdom

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Region
London Inner London — West Westminster
Activity type
Higher or Secondary Education Establishments
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Total cost

The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.

€ 1 999 760,00

Beneficiaries (1)

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