Dynamic Correlations and the Response Function

Matteo Marcuzzi, Andrea Gambassi

The response of physical systems to external perturbations can be used to probe both their equilibrium and nonequilibrium dynamics. While response and correlation functions are related in equilibrium by fluctuation-dissipation theorems, out of equilibrium they provide complementary information on the dynamics. In the past years, a method has been devised to map the quantum dynamics of an isolated extended system after a quench onto a static theory with boundaries in imaginary time; up to now, however, the focus was entirely on symmetrized correlation functions. Here we provide a prescription which, in principle, allows one to retrieve the whole set of relevant dynamical quantities characterizing the evolution, including linear response functions. We illustrate this construction with some relevant examples, showing in the process the emergence of light-cone effects similar to those observed in correlation functions.

M. Bönitz

Xi-Zhen Wu, Fumihiko Sakata, Yizhong Zhuo +1 more

Aiming at exploring microscopic dynamics responsible for the dissipative large-amplitude collective motion, the dynamic response and correlation functions are introduced within the general theory of nuclear coupled-master equations. The theory is based on the microscopic theory of nuclear collective dynamics which has been developed within the time-dependent Hartree-Fock (TDHF) theory for disclosing the complex structure of the TDHF manifold. A systematic numerical method for calculating the dynamic response and correlation functions is proposed. By performing numerical calculation for a simple model Hamiltonian, it is pointed out that the dynamic response function gives important information in understanding the large-amplitude dissipative collective motion which is described by an ensemble of trajectories within the TDHF manifold.

Giorgio Parisi A

Aiichiro Nakano, Setsuo Ichimaru

Time-dependent multiparticle correlation functions and response functions are formulated with the functional derivatives in the grand-canonical ensemble. Equations for the single-particle Green's functions are the Dyson equations describing scattering of the single particles by density-fluctuation excitations. Equations for the density-fluctuation excitations are truncated with a dynamic version of the convolution approximation to triple correlations. A closed set of equations for the Green's functions and excitations are thereby obtained, which constitutes a dynamic hypernetted-chain scheme for the degenerate electron liquids. The formalism is extended also to the description of the spin-dependent response and correlations.