Abstract
 
 
I discuss some effects of (interacting) perturbations to the Hamiltonian of the quantum XY model in the non-equilibrium time evolution after a global quench. At sufficiently large times the perturbations dramatically affect the expectation values of local observables. The leading contribution can be traced back to the breaking of non-abelian integrability, which is manifest at times proportional to the inverse perturbation strength. I describe different scenarios for the time evolution of observables, focusing on the emergence of persistent oscillations. Finally, I point out a scaling behaviour for the time evolution of the entanglement entropies of spin blocks, which is essentially independent of the quench details.