Séminaire de Mathématiques Accessibles

Séminaire à l'Institut Camille Jordan
Orateur: Christophe Garban ( Lyon 1)

Séminaire de Mathématiques Accessibles à l'Institut Camille Jordan :

Des exposés d'1 heure, au rythme d'un exposé par mois, accessibles à un public plus large que les séminaires spécialisés traditionnels.

Public visé :
- au moins tout enseignant chercheur en maths pures et appliquées.
- souvent enseignants chercheurs d'autres disciplines connexes, étudiants...
- ponctuellement, public plus large (lycéens...).

Lundi 25 mars 2024, en salle C 112

Orateur: Christophe Garban ( Lyon 1)

Abstract:
One of the main goals of statistical physics is to observe how spins displayed along a lattice Z^d interact together and fluctuate. When the spins belong to a discrete set (for example the celebrated Ising model where spins \sigma_x belong to {-1,+1}), the nature of the phase transitions which arise as one varies the temperature is now rather well understood. When the spins belong instead to a continuous space (for example the unit circle S^1 for the so-called XY model, the unit sphere S^2 for the classical Heisenberg model etc.), the nature of the phase transitions differs drastically from the discrete symmetry setting. The case where the (continuous) symmetry is non-Abelian is currently more mysterious than when the symmetry is Abelian. In the later case, phase transitions are caused by a change of behaviour of certain monodromies in the system called "vortices". They are called topological phase transitions for this reason.  
In this talk, after an introduction to the mathematics of spin systems with a continuous symmetry, I will present some recent results on these spins systems as well as on models naturally associated with them, such as Coulomb gases and random integer-valued interfaces.

The talk will not require any background in statistical physics/probability. Based on joint works with Juhan Aru, Paul Dario, Avelio Sepúlveda and Tom Spencer.