305 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.
Density functional for pairing with particle number conservation
In this work, a new functional is introduced to treat pairing correlations in
finite many-body systems. Guided by the projected BCS framework, the energy is
written as a functional of occupation numbers. It is shown to generalize the
BCS approach and to provide an alternative to Variation After Projection
framework. Illustrations of the new approach are given for the pairing
Hamiltonian for various particle numbers and coupling strengths. In all case, a
very good agreement with the exact solution is found.Comment: Proceeding of the International Symposium: Forefronts of Researches
in Exotic Nuclear Structures- Niigata201
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
Beyond mean-field calculation for pairing correlation
The recently proposed Symmetry-Conserving Energy Density Functional approach
[G. Hupin, D. Lacroix and M. Bender, Phys. Rev. C84, 014309 (2011)] is applied
to perform Variation After Projection onto good particle number using Skyrme
interaction, including density dependent terms. We present a systematic study
of the Kr and Sn isotopic chains. This approach leads to non-zero pairing in
magic nuclei and a global enhancement of the pairing gap compared to the
original theory that breaks the particle number symmetry. The need to
consistently readjust the pairing effective interaction strength is discussed.Comment: 7 pages, 9 figure
Functional approach for pairing in finite systems: How to define restoration of broken symmetries in Energy Density Functional theory ?
The Multi-Reference Energy Density Functional (MR-EDF) approach (also called
configuration mixing or Generator Coordinate Method), that is commonly used to
treat pairing in finite nuclei and project onto particle number, is
re-analyzed. It is shown that, under certain conditions, the MR-EDF energy can
be interpreted as a functional of the one-body density matrix of the projected
state with good particle number. Based on this observation, we propose a new
approach, called Symmetry-Conserving EDF (SC-EDF), where the breaking and
restoration of symmetry are accounted for simultaneously. We show, that such an
approach is free from pathologies recently observed in MR-EDF and can be used
with a large flexibility on the density dependence of the functional.Comment: proceeding of the conference "Many body correlations from dilute to
dense Nuclear systems", Paris, February 201
On the formulation of functional theory for pairing with particle number restoration
The restoration of particle number within Energy Density Functional theory is
analyzed. It is shown that the standard method based on configuration mixing
leads to a functional of both the projected and non-projected densities. As an
alternative that might be advantageous for mass models, nuclear dynamics and
thermodynamics, we propose to formulate the functional in terms directly of the
one-body and two-body density matrices of the state with good particle number.
Our approach does not contain the pathologies recently observed when restoring
the particle number in an Energy Density Functional framework based on
transition density matrices and can eventually be applied with functionals
having arbitrary density dependencies.Comment: 11 pages, 3 figure
Unified description of Li structure and deuterium-He dynamics with chiral two- and three-nucleon forces
Prototype for the study of weakly bound projectiles colliding on stable
targets, the scattering of deuterium () on He () is an important
milestone in the search for a fundamental understanding of low-energy
reactions. At the same time, it is also important for its role in the Big-bang
nucleosynthesis of Li and applications in the characterization of deuterium
impurities in materials. We present the first unified {\em ab initio} study of
the Li ground state and -He elastic scattering using two- and
three-nucleon forces derived within the framework of chiral effective field
theory. The six-nucleon bound-state and scattering observables are calculated
by means of the no-core shell model with continuum. %and are compared to
available experimental data. We analyze the influence of the dynamic
polarization of the deuterium and of the chiral three-nucleon force, and
examine the role of the continuum degrees of freedom in shaping the low-lying
spectrum of Li. We find that the adopted Hamiltonian correctly predicts the
binding energy of Li, yielding an asymptotic - to -state ratio of the
Li wave function in configuration of in agreement with
the value determined from a phase shift analysis of Li+He elastic
scattering, but overestimates the excitation energy of the first state by
keV. The bulk of the computed differential cross section is in good
agreement with data.Comment: 5 pages, 5 figure
Advances in the ab initio description of nuclear three-cluster systems
We introduce the extension of the ab initio no-core shell model with
continuum to describe three-body cluster systems. We present results for the
ground state of 6He and show improvements with respect to the description
obtained within the no-core shell model and the no-core shell model/resonating
group methods.Comment: Proceedings of the 21st International Conference on Few-Body Problems
in Physics. May 18-22, 2015. Chicago, Illinois, US
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