8,447 research outputs found
Quantum Monte-Carlo method applied to Non-Markovian barrier transmission
In nuclear fusion and fission, fluctuation and dissipation arise due to the
coupling of collective degrees of freedom with internal excitations. Close to
the barrier, both quantum, statistical and non-Markovian effects are expected
to be important. In this work, a new approach based on quantum Monte-Carlo
addressing this problem is presented. The exact dynamics of a system coupled to
an environment is replaced by a set of stochastic evolutions of the system
density. The quantum Monte-Carlo method is applied to systems with quadratic
potentials. In all range of temperature and coupling, the stochastic method
matches the exact evolution showing that non-Markovian effects can be simulated
accurately. A comparison with other theories like Nakajima-Zwanzig or
Time-ConvolutionLess ones shows that only the latter can be competitive if the
expansion in terms of coupling constant is made at least to fourth order. A
systematic study of the inverted parabola case is made at different
temperatures and coupling constants. The asymptotic passing probability is
estimated in different approaches including the Markovian limit. Large
differences with the exact result are seen in the latter case or when only
second order in the coupling strength is considered as it is generally assumed
in nuclear transport models. On opposite, if fourth order in the coupling or
quantum Monte-Carlo method is used, a perfect agreement is obtained.Comment: 10 pages, 6 figures, to be published in Phys. Rev.
Non-Markovian effects in quantum system: an exact stochastic mean-field treatment
A quantum Monte-Carlo is proposed to describe fusion/fission processes when
fluctuation and dissipation, with memory effects, are important. The new theory
is illustrated for systems with inverted harmonic potentials coupled to a
heat-bath.Comment: Proceedings of the international conference: "Nuclear Structure and
related topics, Dubna, June (2009
Configuration mixing within the energy density functional formalism: pathologies and cures
Configuration mixing calculations performed in terms of the Skyrme/Gogny
Energy Density Functional (EDF) rely on extending the Single-Reference energy
functional into non-diagonal EDF kernels. The standard way to do so, based on
an analogy with the pure Hamiltonian case and the use of the generalized Wick
theorem, is responsible for the recently observed divergences and steps in
Multi-Reference calculations. We summarize here the minimal solution to this
problem recently proposed [Lacroix et al, arXiv:0809.2041] and applied with
success to particle number restoration[Bender et al, arXiv:0809.2045]. Such a
regularization method provides suitable corrections of pathologies for EDF
depending on integer powers of the density. The specific case of fractional
powers of the density[Duguet et al, arXiv:0809.2049] is also discussed.Comment: 5 pages, Proceedings of the French-Japanese Symposium, September
2008. To be published in Int. J. of Mod. Phys.
Quantal Extension of Mean-Field Dynamics
A method is presented for numerical implementation of the extended TDHF
theory in which two-body correlations beyond the mean-field approximation are
incorporated in the form of a quantal collision term. The method is tested in a
model problem in which the exact solution can be obtained numerically. Whereas
the usual TDHF fails to reproduce the long time evolution, a very good
agreement is found between the extended TDHF and the exact solution.Comment: 22 Latex pages including 7 figure
A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length
Inspired by the low--density Lee-Yang expansion for the energy of a dilute
Fermi gas of density and momentum , we introduce here a
Skyrme--type functional that contains only -wave terms and provides, at the
mean--field level, (i) a satisfactory equation of state for neutron matter from
extremely low densities up to densities close to the equilibrium point, and
(ii) a good--quality equation of state for symmetric matter at density scales
around the saturation point. This is achieved by using a density--dependent
neutron-neutron scattering length ) which satisfies the low--density
limit (for Fermi momenta going to zero) and has a density dependence tuned in
such a way that the low--density constraint is satisfied
at all density scales.Comment: 5 figure
From dilute matter to the equilibrium point in the energy--density--functional theory
Due to the large value of the scattering length in nuclear systems, standard
density--functional theories based on effective interactions usually fail to
reproduce the nuclear Fermi liquid behavior both at very low densities and
close to equilibrium. Guided on one side by the success of the Skyrme density
functional and, on the other side, by resummation techniques used in Effective
Field Theories for systems with large scattering lengths, a new energy--density
functional is proposed. This functional, adjusted on microscopic calculations,
reproduces the nuclear equations of state of neutron and symmetric matter at
various densities. Furthermore, it provides reasonable saturation properties as
well as an appropriate density dependence for the symmetry energy.Comment: 4 figures, 2 table
Nucleon exchange in heavy-ion collisions within stochastic mean-field approach
Nucleon exchange mechanism is investigated in deep-inelastic symmetric
heavy-ion collisions in the basis of the Stochastic Mean-Field approach. By
extending the previous work to off-central collisions, analytical expression is
deduced for diffusion coefficient of nucleon exchange mechanism. Numerical
calculations are carried out for Ca + Ca and Zr +
Zr systems and the results are compared with the phenomenological
nucleon exchange model. Also, calculations are compared with the available
experimental results of deep-inelastic collisions between calcium nuclei.Comment: 8 pages, 7 figure
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