Theory of open Fermi systems for describing atomic nuclei and nuclear reactions

A.B. Migdal, S. A. Moszkowski

B. H. Brandow

A. Díaz-Torres, Paraskevi Demetriou, Rauno Julin +1 more

Atomic nuclei are complex, quantum many‐body systems whose structure manifests itself through intrinsic quantum states associated with different excitation modes or degrees of freedom. Collective modes (vibration and/or rotation) dominate at low energy (near the ground‐state). The associated states are usually employed, within a truncated model space, as a basis in (coherent) coupled channels approaches to low‐energy reaction dynamics. However, excluded states can be essential, and their effects on the open (nuclear) system dynamics are usually treated through complex potentials. Is this a complete description of open system dynamics? Does it include effects of quantum decoherence? Can decoherence be manifested in reaction observables? In this contribution, I discuss these issues and the main ideas of a coupled‐channels density‐matrix approach that makes it possible to quantify the role and importance of quantum decoherence in low‐energy nuclear reaction dynamics. Topical applications, which refer to understanding the astrophysically important collision 12C+12C and achieving a unified quantum dynamical description of relevant reaction processes of weakly‐bound nuclei, are highlighted.

H. Kuemmel, K.H. Lührmann, John G. Zabolitzky +2 more

Vazgen Valerikovich Sargsyan, Z. Kanokov, G. G. Adamian +1 more

Quantum diffusion equations with time-dependent transport coefficients are derived from generalized non-Markovian Langevin equations. Generalized fluctuation-dissipation relations and analytical formulas for calculating friction and diffusion coefficients in nuclear processes are obtained. The asymptotics of the transport coefficients and of the correlation functions are investigated. The problem of correlation decay in quantum dissipative systems is studied. A comparative analysis of diffusion coefficients for the harmonic and inverted oscillators is performed. The role of quantum statistical effects during passage through a parabolic potential barrier is investigated. Sets of diffusion coefficient assuring the purity of states at any time instant are found in cases of non-Markovian dynamics. The influence of different sets of transport coefficients on the rate of decay from a metastable state is studied in the framework of the master equation for reduced density matrices describing open quantum systems. The approach developed is applied to investigation of fission processes and the processes of projectile-nuclei capture by target nuclei for bombarding energies in the vicinity of the Coulomb barrier. The influence of dissipation and fluctuation on these processes is taken into account in a self-consistent way. The evaporation residue cross sections for asymmetric fusion reactions are calculated from the derived capture probabilities averaged over all orientations of the deformed projectile and target nuclei.

A. Díaz-Torres

Atomic nuclei are complex, quantum many-body systems whose structure manifests itself through intrinsic quantum states associated with different excitation modes or degrees of freedom.Collective modes (vibration and/or rotation) dominate at low energy (near the ground-state).The associated states are usually employed, within a truncated model space, as a basis in (coherent) coupled channels approaches to low-energy reaction dynamics.However, excluded non-collective states can be essential, and their effects on the open (nuclear) system dynamics are usually treated through complex potentials.Is this a complete description of open system dynamics?Does it include effects of quantum decoherence?Can decoherence be manifested in reaction observables?This paper discusses these issues and the main ideas of a coupled-channels density-matrix approach that makes it possible to quantify the role and importance of quantum decoherence in low-energy nuclear reaction dynamics.Some topical applications are highlighted.