Operator local quenches in massive scalar field theory

In this talk, we introduce the notion of quantum quenches in relativistic quantum field theory (QFT). Generically, quantum quenches correspond to a sudden change in a quantum system, which brings it out of equilibrium. We study the particular type of quantum quenches, which is described by the operator local quench protocol, where a quantum state becomes excited by a local insertion of a field operator at some spacetime point. These out-of-equilibrium processes are well-studied in a two-dimensional QFT, which has an underlying conformal symmetry — conformal field theory (CFT). We give a short but comprehensive overview of the dynamics of excited states in this theory, and then extend the consideration to an arbitrary number of spacetime dimensions, as well as to the simplest non-conformal case — the massive scalar field theory. We also generalize the CFT results to the two-dimensional massive scalar field theory with the compact spatial dimension. By probing different correlation functions, corresponding to various physical observables, we reveal dynamical features of the theory, which cannot be observed in the equilibrium regime, and compare the results with those in $d = 2$ CFT.