E.S. Hernández

Asymmetric rotor with variable moment-of-inertia model

Abstract An asymmetric rotor with variable moment-of-inertia (AROVMI) model is proposed to permit the simultaneous fitting of both the ground state and γ-vibrational bands in doubly even nuclei. Only those nuclei for which these bands are well established are analysed. The results obtained from a least-squares fitting procedure are compared with the latest available experimental data and with those calculated with the variable moment-of-inertia (VMI) model. The theoretical analysis shows a good overall agreement with experimental data into the region spanned from the very hard rotors up to the very good vibrators.

Finite temperature RPA in symmetric nuclear matter with Skyrme interactions

Abstract We investigate the RPA response for thermally excited nuclear matter interacting through Skyrme interactions. Closed analytical expressions are obtained for the dynamic susceptibility in each spin-isopspin channel. We compute the strength as a function of energy, transferred momentum and temperature, and examine the evolution of collective states, when present. The energy weighted sum rules M k , for k = −1, 1 and 3 are also shown to possess explicit expressions as functions of both momentum and temperature. It is seen that thermal effects on the susceptibility are as important as dynamical ones associated to momentum transfer, at least for temperatures as high as 20% of the Fermi energy.

Disappearance of zero sound in asymmetric nuclear matter

Abstract We investigate the thermal RPA response of asymmetric nuclear matter interacting through a Skyrme interaction. For every spin-isospin channel, the evolution of the zero sound as a function of both neutron excess and temperature is analyzed.

Phase space fluctuations and dynamics of fluctuations of collective variables

Abstract Within the framework of theoretical approaches based on stochastic transport equation of one-body distribution function, a numerical treatment of the fluctuations of collective observables is studied and checked in comparison with analytical results either at equilibrium or close to it.

Spectral and thermodynamical properties of symmetric nuclear matter with Gogny interaction

Abstract The finite ranges effect of an effective force on the single particle properties and the particle-hole effective interaction are investigated in a wide interval of temperatures. The calculations are performed in a framework of a thermal Hartree-Fock method using the D1-Gogny density dependent interaction. First, the behaviour of the single particle potential, effective mass and the momentum distribution is discussed. The competition between statistical correlations and mean field effects is studied by analyzing the relative momentum distribution and the two-body distribution function. Secondly, a possible extension of the Landau Fermi liquid theory to finite temperatures is discussed in the context of symmetric nuclear matter. Special attention is devoted to the meaning of the Landau parameters and to the requirements for thermodynamic stability. In particular, the relation between the nuclear incompressibility and the F 0 ss - Landau amplitude at finite temperatures is carefully analyzed.

Collective coordinates as open systems: (I). Existence conditions for frictional hamiltonians

Abstract We examine the time evolution of an object coupled to a heat reservoir at zero temperature in the framework of general master and kinetic equations for open systems. As we specialize to the particular set of solutions that represents pure states, we are led to a frictional Schrodinger equation that is free from either heuristic hypotheses or perturbation-like approximations. The generator of the evolution of damped pure states, namely the frictional hamiltonian. can be seen to be non-hermitian and to satisfy an integral, non-linear equation. The Schrodinger equation for damped wave packets is valid at all times, provided that a strongly restrictive condition holds. This condition offers an interesting interpretation in the general case. while in the weak-coupling limit, it could be said to provide a quantal version of a fluctuation-dissipation theorem.

Kinetic parameters in the nuclear Fermi gas model at finite temperatures

Abstract The validity of the dilute Fermi gas model for the evaluation of transport parameters in nuclear matter is examined in the framework of quantal kinetic theory. The consistency of the approximations involved in the calculations of the collision rate between weakly interacting nucleons is analyzed, considering several ways of representing the residual interaction, namely via zero-range, medium-range, and short-momentum-spread forces. The theoretical mean free path is derived, with a proper handling of the collision kernel in a nuclear kinetic equation, and computed as a function of temperature and single-particle energy for the interactions in the weak-coupling approximation. The competition among interaction range and quantal and kinetic length scales is discussed.

Response of asymmetric nuclear matter to isospin-flip probes

Abstract We investigate the RPA response of asymmetric nuclear matter to external fields which induce charge exchange between nucleons, both at zero and finite temperature. Closed expressions are obtained for the RPA response in each spin channel when the nucleon–nucleon interaction is of the Skyrme type. Exchange terms are fully taken into account. We consider the transferred momentum, asymmetry and temperature as the relevant parameters of our study. Special emphasis is given to the role of neutron excess in relation to the collective states at low momentum.

From stochastic phase-space evolution to brownian motion in collective space

Abstract Within the framework of stochastic transport equations in phase space, we study the dynamics of fluctuations on collective variables in homogeneous fermion systems. The transport coefficients are formally deduced in the relaxation-time approximation and a general method to compute dynamically the dispersions of collective observables is proposed as a set of coupled equations: respectively, the BUU/Landau-Vlasov equation for the average phase-space trajectories and the equations for the averages and dispersions of the observables. Independently, we derive the general covariance matrix of phase-space fluctuations and then by projection, the dispersion on collective variables at equilibrium. Detailed numerical applications of the formalism are given; they show that the dynamics of fluctuations can be extracted from noisy numerical simulations and that the leading parameter for collective fluctuations is the excitation energy, whatever is its degree of thermalization.

Collective coordinates as open systems: (II). Time-scale for pure-state propagation

Abstract In the frame of a general master equation, we investigate the condition for the propagation of pure-state wave packets conditioned to the gain-loss competition between the different components. If a perturbative approach is adopted, it is shown that the hamiltonian type of evolution is destroyed within the microscopic time-scale, thus inhibiting the possibility of simulating the motion via a frictional Schrodinger equation as frequently undertaken.