Project description
Expanding motivic cohomology theory with topological coefficients
Motives are abstract, foundational objects in modern algebraic geometry, introduced to unify various cohomology theories and enhance understanding of algebraic varieties. In Voevodsky’s category of étale motives, topological rings can be considered as coefficients. Realisation functors transform abstract, often ‘hidden’ motivic structures into computable data such as cohomology groups. Ensuring these realisation functors are well behaved remains an open challenge. With the support of the Marie Skłodowska-Curie Actions programme, the Solid Motives project aims to construct such an extension by merging Voevodsky’s motivic framework with the recently developed theory of condensed mathematics by Clausen and Scholze. The resulting machinery will be applied to a long-standing open problem: proving that certain topological invariants of algebraic varieties in positive characteristic are independent of an auxiliary prime number.
Objective
The main goal of this project is to construct an enlargement of Voevodsky's category of étale motives in which topological rings can be considered as coefficients. In this formalism, ℓ-adic realization functors will be particularly well-behaved and simply given by changing the ring of coefficients to the topological ring of ℓ-adic numbers. This will be achieved by merging Voevodsky's ideas with the recent work of Clausen–Scholze on condensed mathematics. A key technical challenge is to generalize the notion of a solid abelian group to a much broader context so that it also applies to categories of motivic nature. One of the key ingredients I will use is the machinery of internal higher categories, developed in joint work with Martini.
I will prove that the categories I construct possess many of the convenient properties one expects. Specifically, I will show that they are equipped with a well-behaved formalism of six operations and that a suitable version of the Suslin–Voevodsky rigidity theorem holds. I then intend to use this new machinery to address the question of the independence of ℓ in Betti numbers for varieties of positive characteristic—a long-standing and difficult open problem—following ideas of Cisinski. The key property I will exploit is that, in this new formalism, the motive representing ℓ-adic cohomology is stable under base change, which is not the case in the setting of usual étale motives.
I will also use some of the convenient properties of ℓ-adic realization in this setup to construct new categories of Nori motives with spectral coefficients, providing new evidence for a conjecture of Ayoub.
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Project’s keywords as indicated by the project coordinator. Not to be confused with the EuroSciVoc taxonomy (Fields of science)
Programme(s)
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HORIZON.1.2 - Marie Skłodowska-Curie Actions (MSCA)
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Calls for proposals are divided into topics. A topic defines a specific subject or area for which applicants can submit proposals. The description of a topic comprises its specific scope and the expected impact of the funded project.
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Funding scheme (or “Type of Action”) inside a programme with common features. It specifies: the scope of what is funded; the reimbursement rate; specific evaluation criteria to qualify for funding; and the use of simplified forms of costs like lump sums.
HORIZON-TMA-MSCA-PF-EF - HORIZON TMA MSCA Postdoctoral Fellowships - European Fellowships
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Call for proposal
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(opens in new window) HORIZON-MSCA-2025-PF
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1165 KOBENHAVN
Denmark
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