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Noncommutative ergodic theory of higher rank lattices

Project description

Study explores noncommutative ergodic theory’s impact on Lie group rigidity

Noncommutative ergodic theory explores the behaviour of dynamical systems through operator algebras. Recent advancements in this field have unveiled significant insights, such as a noncommutative version of Nevo-Zimmer’s structure theorem, enhancing understanding of ergodic theory, topological dynamics, unitary representation theory, and operator algebras associated with higher-rank lattices. Key achievements include a noncommutative analogue of Margulis’ factor theorem, providing strong evidence for Connes’ rigidity conjecture and highlighting interactions between discrete subgroups of semi-simple Lie groups and operator algebras. The ERC-funded NET project aims to explore character rigidity and the dynamics of positive definite functions while also developing methods to tackle Connes’ conjecture. Project results could potentially reveal new rigidity phenomena in higher-rank semi-simple Lie groups.

Objective

Noncommutative ergodic theory of higher rank lattices is a current topic that has seen several exciting developments in the last five years. Among these recent advancements, in joint work with Rmi Boutonnet (2019), we proved a noncommutative analogue of Nevo-Zimmer's structure theorem for actions of higher rank lattices on von Neumann algebras. First of all, we derived several novel applications to ergodic theory, topological dynamics, unitary representation theory and operator algebras associated with higher rank lattices. Then we obtained a noncommutative analogue of Margulis' factor theorem that provides strong evidence towards Connes' rigidity conjecture for the group von Neumann algebra of higher rank lattices. These results revealed deep and unexpected interactions between the field of discrete subgroups of semisimple Lie groups and the field of operator algebras.

In this research project, I plan to build upon these recent achievements to develop new directions in noncommutative ergodic theory of higher rank lattices. This research proposal is centered around two main interconnected themes.

Firstly, I plan to work on several problems and conjectures around the dynamics of the space of positive definite functions and character rigidity for higher rank lattices. These include the classification of characters for higher rank lattices of product type, and more general lattices with dense projections in product groups as well as stiffness results for stationary positive definite functions.

Secondly, drawing inspiration from Margulis' superrigidity theorem, I plan to tackle Connes' rigidity conjecture for higher rank lattices by developing a novel strategy combining techniques from boundary theory, C*-algebras and von Neumann algebras. These methods will lead to new rigidity phenomena for operator algebras arising from irreducible lattices in higher rank semisimple connected Lie groups.

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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-2023-ADG

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Host institution

ECOLE NORMALE SUPERIEURE
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.

€ 2 140 250,00
Address
45, RUE D'ULM
75230 Paris
France

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Region
Ile-de-France Ile-de-France Paris
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.

€ 2 140 250,00

Beneficiaries (1)

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