Physics (Internal)

Equilibration and coarsening in the quantum O(N) model

This event is part of the Condensed Matter Theory Seminar Series.

Abstract: The quantum O(N) model in the infinite N limit is a paradigm for continuous symmetry-breaking. Its phase diagram provides an excellent qualitative guide to the equilibrium physics of symmetry breaking across spatial dimensions. In this talk, I will investigate the physics of this model out of equilibrium, and in particular, its response to global quenches starting from the disordered phase. If the model were to equilibrate, the late time state would follow from the finite temperature phase diagram. At infinite N, however, the model cannot equilibrate to a Gibbs ensemble due to the presence of an infinite number of conserved quantities. Remarkably, I will show that it also fails to relax to a generalized Gibbs ensemble consistent with these conserved quantities. Nevertheless, the late time states following quenches bear strong signatures of the equilibrium phase diagram. For example, the model exhibits coarsening to a non-equilibrium critical state only in dimensions d>2, that is, if the equilibrium phase diagram contains an ordered phase at non-zero temperature.