2D Critical Quench, Thermalization and Non-Universality

I will talk about our last paper and our current work. In arXiv: 1501.04580, we studied the long time behaviour of local observables following a quantum quench in 1+1 dimensional conformal field theories possessing additional conserved charges besides the energy. We showed exponential approach to equilibrium of finite sub-interval characterized by a temperature and chemical potentials defined in terms of the quenched state. In our ongoing work, we compute the exact wavefunction that results from a quantum quench to a vanishing mass, in a large class of examples The resulting wavefunction is of a generalized Calabrese-Cardy form i.e., conformal boundary state deformed by an infinite number of charges. Special squeezed states with small chemical potentials show equilibration to a Generalized Gibbs Ensemble(GGE) as proved in the above mentioned paper. By contrast, with general pre-quench states, including the ground state, the chemical potentials are not small; exact correlators in these cases, although equilibrating at long times, do not generically have a simple thermal or GGE form even at large distances. The main lesson is that in 2D critical quench, long time and large distance physics can be sensitive to perturbations by high dimension operators, contrasting general Wilsonian lore.