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Geometric Structure of Lattice Spin O(N) models

Objective

Statistical mechanics is concerned with the emergent macroscopic behaviour of systems consisting of interacting microscopic particles. Lattice models form a subclass of such systems where the particles are placed on a lattice (grid), and provide a mathematical framework for studying this emergent behaviour. We are particularly interested in phase transitions, where a small change in the parameters of the model leads to a radical change in the macroscopic behaviour of the system.

In lattice models, the key quantities (e.g. correlation functions) are often encoded in terms of random geometrical objects. In the special case of models with a percolation representation (e.g. Bernoulli percolation, the Ising model), spectacular progress has been made in the past decades. In a large number of natural models, however, the relevant geometrical objects are not clusters (connected components of random subgraphs of the lattice), but rather random families of loops and paths on the lattice (e.g. the XY model, the Heisenberg model, height functions).

Recent insights suggest that striking progress on loop-based models can be made in the next few years. The objective of this project is to break new ground on the fundamental understanding of phase transitions via structural changes in the random loops. This will require significant innovations, combining techniques from probability, combinatorics, analysis, and mathematical physics. Our ambition is to make breakthrough progress on open problems in three central areas:
* The Berezinskii--Kosterlitz--Thouless transition (which led to the 2016 physics Nobel Prize);
* Phase transitions in the XY model in dimension three and higher;
* The Polyakov conjecture for the two-dimensional Heisenberg model.
Even limited progress would clarify the mathematics of critical phenomena of lattice models, which serve as pillars for modern theoretical physics.

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Funding Scheme

HORIZON-ERC - HORIZON ERC Grants

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Call for proposal

(opens in new window) ERC-2026-STG

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Host institution

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
Net EU contribution
€ 1 432 907,00
Address
RUE MICHEL ANGE 3
75794 Paris
France
Region
Ile-de-France Ile-de-France Paris
Activity type
Research Organisations
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Total cost
€ 1 432 907,00

Beneficiaries (1)