Regular and irregular dynamics after local quenches in massive scalar field theory

We study the energy density dynamics following the operator local quench in the theory of a free massive scalar field. In our setup, the local quench is defined as insertion of a field operator at some spacetime point. This produces a local excitation taking the system out of equilibrium. The known results state that in two-dimensional CFT, such perturbation propagates as a soliton along the light cone. We generalize this model to the simplest non-conformal cases. We obtain that the dynamics of the energy density occurs in several regimes with transition governed by the scalar field mass. We also consider the theory in finite volume with the background spacetime represented by a two-dimensional cylinder. In this model, the character of the perturbation evolution is regular on large time scales if the mass is small compared to the circumference of the cylinder. However, with increase of the mass parameter, it changes to complicated behaviour, showing chaotic-like interchange of damping and revival of the energy density amplitude.