Open Quantum Dynamics with Nonlinearly Realized Symmetries 

In the context of effective description of dissipative phenomena, I will consider an open mechanical system with degrees of freedom belonging to a group, e.g. rigid body in a thermal bath. In the first part of the talk, I will introduce the effective (in-in) action that depends only on the system's degrees of freedom without explicit dependence on the bath. Its structure will be fixed by the time reversal and the group symmetry. I will discuss the phenomenologically important limits of linear response and of ohmic dissipation and the constraints posed by these limits on the form of the effective action. I will illustrate everything on a particular example. In the second part of the talk, for the case of ohmic dissipation, I will introduce the Universal bath: a model with an in-out action in one extra dimension that reproduces the quantum dissipative mechanics of the system, once you integrate out the extra dimension. Finally, I will discuss the generalizations and the potential uses of both the effective in-in action and the Universal bath.