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Search Results: 1 - 10 of 2660 matches for " Guillaume Lacroix "
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Exact Stochastic Mean-Field dynamics
Denis Lacroix,Guillaume Hupin
Physics , 2008, DOI: 10.1063/1.3108765
Abstract: The exact evolution of a system coupled to a complex environment can be described by a stochastic mean-field evolution of the reduced system density. The formalism developed in Ref. [D.Lacroix, Phys. Rev. E77, 041126 (2008)] is illustrated in the Caldeira-Leggett model where a harmonic oscillator is coupled to a bath of harmonic oscillators. Similar exact reformulation could be used to extend mean-field transport theories in Many-body systems and incorporate two-body correlations beyond the mean-field one. The connection between open quantum system and closed many-body problem is discussed.
Density functional for pairing with particle number conservation
Denis Lacroix,Guillaume Hupin
Physics , 2010, DOI: 10.1142/S0217732310000484
Abstract: 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.
Density-matrix functionals for pairing in mesoscopic superconductors
Denis Lacroix,Guillaume Hupin
Physics , 2010, DOI: 10.1103/PhysRevB.82.144509
Abstract: A functional theory based on single-particle occupation numbers is developed for pairing. This functional, that generalizes the BCS approach, directly incorporates corrections due to particle number conservation. The functional is benchmarked with the pairing Hamiltonian and reproduces perfectly the energy for any particle number and coupling.
Beyond mean-field calculation for pairing correlation
Guillaume Hupin,Denis Lacroix
Physics , 2012,
Abstract: 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.
On the application of symmetry breaking and its restoration to treat pairing correlation in finite nuclei
Guillaume Hupin,Denis Lacroix
Physics , 2012, DOI: 10.1143/PTPS.196.250
Abstract: An alternative approach to symmetry restoration within Energy Density Functional, the Symmetry-Conserving EDF is discussed. In this approach, the energy is directly written in terms of the degrees of freedom encoded in the one-, two-... body density matrices of the state having good quantum numbers. The SC-EDF framework is illustrated within Projection After and Before variation applied to particle number restoration.
Systematic of isovector and isoscalar giant quadrupole resonances in normal and superfluid deformed nuclei
Guillaume Scamps,Denis Lacroix
Physics , 2014, DOI: 10.1103/PhysRevC.89.034314
Abstract: The systematic study of isoscalar (IS) and isovector (IV) giant quadrupole responses (GQR) in normal and superfluid nuclei presented in [G. Scamps and D. Lacroix, Phys. Rev. 88, 044310 (2013)] is extended to the case of axially deformed and triaxial nuclei. The static and dynamical energy density functional based on Skyrme effective interaction are used to study static properties and dynamical response functions over the whole nuclear chart. Among the 749 nuclei that are considered, 301 and 65 are respectively found to be prolate and oblate while 54 do not present any symmetry axis. For these nuclei, the IS- and IV-GQR response functions are systematically obtained. In these nuclei, different aspects related to the interplay between deformation and collective motion are studied. We show that some aspects like the fragmentation of the response induced by deformation effects in axially symmetric and triaxial nuclei can be rather well understood using simple arguments. Besides this simplicity, more complex effects show up like the appearance of non-trivial deformation effects on the collective motion damping or the influence of hexadecapole or higher-orders effects. A specific study is made on the triaxial nuclei where the absence of symmetry axis adds further complexity to the nuclear response. The relative importance of geometric deformation effects and coupling to other vibrational modes are discussed.
Effect of pairing on transfer and fusion reactions
Guillaume Scamps,Denis Lacroix
Physics , 2014, DOI: 10.1051/epjconf/20158600042
Abstract: In the present contribution, the effect of pairing on nuclear transfer and fusion reactions close to the Coulomb barrier is discussed. A Time-Dependent Hartree-Fock + BCS (TDHF+BCS) microscopic theory has been developed to incorporate pairing. One- and two-particle transfer probabilities can be obtained showing the importance of pairing. The calculated transfer probabilities are compared to the recent experimental results obtained for the $^{96}$Zr+$^{40}$Ca. Reactions involving the $^{18}$O with lead isotopes are also presented, that are also of current experimental interest. Finally, a study of the fusion barrier height predicted with the TDHF+BCS theory is compared to the experimental values for the $^{40,44,48}$Ca+$^{40}$Ca reactions.
Description of Pairing correlation in Many-Body finite systems with density functional theory
Guillaume Hupin,Denis Lacroix
Physics , 2010, DOI: 10.1103/PhysRevC.83.024317
Abstract: Different steps leading to the new functional for pairing based on natural orbitals and occupancies proposed in ref. [D. Lacroix and G. Hupin, arXiv:1003.2860] are carefully analyzed. Properties of quasi-particle states projected onto good particle number are first reviewed. These properties are used (i) to prove the existence of such a functional (ii) to provide an explicit functional through a 1/N expansion starting from the BCS approach (iii) to give a compact form of the functional summing up all orders in the expansion. The functional is benchmarked in the case of the picked fence pairing Hamiltonian where even and odd systems, using blocking technique are studied, at various particle number and coupling strength, with uniform and random single-particle level spacing. In all cases, a very good agreement is found with a deviation inferior to 1% compared to the exact energy.
Effect of pairing on one- and two-nucleon transfer below the Coulomb barrier: a time-dependent microscopic description
Guillaume Scamps,Denis Lacroix
Physics , 2012, DOI: 10.1103/PhysRevC.87.014605
Abstract: The effect of pairing correlation on transfer reaction below the Coulomb barrier is investigated qualitatively and quantitatively using a simplified version of the Time-Dependent Hartree-Fock + BCS approach. The effect of particle number symmetry breaking on the description of reaction and dedicated methods to extract one and two-nucleon transfer probabilities (P_{1n} and P_{2n}) in a particle number symmetry breaking approach are discussed. Influence of pairing is systematically investigated in the ^{40}Ca+ ^{40,42,44,46,48,50}Ca reactions. A strong enhancement of the two-particle transfer probabilities due to initial pairing correlations is observed. This enhancement induces an increase of the ratio of probabilities P_{2n} / (P_{1n})^2 compared to the case with no pairing. It is shown that this ratio increases strongly as the center of mass energy decreases with a value that could be larger than ten in the deep sub-barrier regime. An analysis of the pair transfer sensitivity to the type of pairing interaction, namely surface, mixed or volume, used in the theory is made. It is found that the pair transfer is globally insensitive to the type of force and mainly depends on the pairing interaction strength.
Effect of pairing on nuclear dynamic
Scamps Guillaume,Lacroix Denis
Physics , 2013,
Abstract: The effect of pairing on small and large amplitude dynamics is discussed. Pairing correlation is treated in a fully microscopic transport theory using a simplified BCS version of the Time-Dependent Hartree-Fock Bogolyubov (TDHFB) theory. The approach is applied to study the Giant Dipole and Giant Quadrupole Resonance in spherical and/or deformed magnesium isotopes showing very good agreement with QRPA theory. The present framework also provides a consistent approach to describe nuclear reactions around the Coulomb barrier. As an illustration, the influence of pairing correlations on multi-nucleon transfer is studied for reactions at sub-barrier energy.
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