The (complete) Generalized Gibbs Ensemble in the Heisenberg spin chains

Rövid cím: 
Generalized Gibbs Ens. in Heisenberg spin chains
2016. 11. 11. 10:15
BME Fizikai Intézet, Elméleti Fizika Tanszék, Budafoki út 8. F-épület, III lépcsőház, szemináriumi szoba
Balázs Pozsgay (BUTE Dept. Theor. Phys.)

We will consider non-equilibrium situations (and in particular quantum quenches) in the XXZ and XXX Heisenberg spin chains, which are one of the most important integrable models. It was suggested, that in such models the physical behaviour in the long-time limit can be described by the so-called Generalized Gibbs Ensemble (GGE). In contrast to the usual Gibbs ensemble the GGE also includes the higher conserved charges of the models. Whereas it was shown by our group in 2014 that the traditional approach to the GGE fails, later it was found that a broader GGE (which includes all the recently found ultra-local charges) can indeed give a correct description. In this talk we discuss certain aspects of this question. What does it mean to have infinite number of charges in an ensemble? In what sense is it complete? What is the range of its applicability? We also discuss the seemingly technical question of the validity of the so-called Y-system equations, which nevertheless has important consequences for the practical solution of the quench problems.