From microscopic to macroscopic dynamics in mean-field theory: effect of neutron skin on fusion barrier and dissipation

In this work, we introduce a new method to reduce the microscopic mean-field theory to a classical macroscopic dynamics during the initial stage of fusion reactions. We show that TDHF (Time-dependent Hartree-Fock) could be a useful tool to gain information on fusion barriers as well as on one-body dissipation effects. We apply the mean-field theory to the case of head-on reaction between $^{16}$O and $^{16,22,24,28}$O in order to quantify the effect of neutron skin on fusion. We show that the determination of fusion barrier requires, in addition to a precise knowledge of the relative distance between the center of mass of the two fusing nuclei, the introduction of an additional collective coordinate that explicitly breaks the neutron-proton symmetry. In this context, we estimate the position, height and diffuseness of the barrier as well as the one-body friction and show that a global enhancement of the fusion cross-section is expected in neutron rich nuclei.Comment: 9 ps pages including 9 figure

Introduction - Strong interaction in the nuclear medium: new trends

Recent achievements in nuclear forces theory open new perspectives for the next decade of low energy nuclear physics, bringing together people from very different communities. Although many developments remain to be done, the possibility to directly use QCD to describe nuclear system is a major challenge that is within reach. In this introduction to the 2009 International Joliot-Curie School (EJC2009), new trends in the strong nuclear interaction are summarized starting from quarks and ending with finite or infinite nuclear systems. At different energy scales, selected new concepts and ideas have been discussed in a rather simple way. Recent advances in the theory of nuclear forces, thanks to chiral perturbation and effective field theories, have led to a new generation of strong nuclear interaction particularly suited to low energy nuclear physics. The interesting aspects of new interactions compared to conventional forces are underlined. Recent achievements in ab initio theories that directly start from the bare nucleon-nucleon interaction and their key role to understand the three-body force are illustrated. Finally, future perspectives for standard nuclear physics theories, namely Shell Model and Energy Density Functional, are discussed.Comment: 26 pages, 28 figures--Introduction Lecture to the 2009 International Joliot-Curie School, Lacanau, France, 27 Sept.-3 Oct. 200

Quantum Monte-Carlo methods and exact treatment of the two-body problem with Hartree-Fock Bogoliubov states

In this article, we show that the exact two-body problem can be replaced by quantum jumps between densities written as D=| \Psi_a \right> \left< \Psi_b | where | \Psi_a \right> and | \Psi_b \right> are vacuum for different quasi-particles operators. It is shown that the stochastic process can be written as a Stochastic Time-Dependent Hartree-Fock Bogoliubov theory (Stochastic TDHFB) for the generalized density ${\cal R}$ associated to $D$ where ${\cal R}^2 = {\cal R}$ along each stochastic trajectory.Comment: 5 page

Effect of pairing on one- and two-nucleon transfer below the Coulomb barrier: a time-dependent microscopic description

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.Comment: 12 pages, 10 figure

Assessing the Impact of a Wage Subsidy for Single Parents on Social Assistance in Canada

In 2002 the Quebec government implemented the "Action Emploi" (AE) program aimed at making work pay for long-term social assistance recipients (SA). AE offered a generous wage subsidy that could last up to three years to recipients who found a full-time job within twelve months. The program was implemented on an experimental basis for a single year. Based on little empirical evidence, a slightly modified version of the program was implemented on permanent basis in May 2008. The paper investigates the impact of the temporary program by focusing on the labour market transitions of the targeted population starting one year before the implementation of the program and up until the end of 2005. We use a multi-state multi-episode model. The endogeneity of the participation status is accounted for by treating AE as a distinct state and by allowing correlated unobserved factors to affect the transitions. The model is estimated by the method of simulated moments. Our results show that AE has indeed increased the duration of Off-SA spells and decreased the duration of SA spells slightly. There is also some evidence that the response to the program varies considerably with unobserved individual characteristics.multi-state multi-episode transition model, social assistance, wage subsidy

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

Assessing the Impact of a Wage Subsidy for Single Parents on Social Assistance

In 2002 the Quebec government implemented the "Action Emploi" (AE) program aimed at making work pay for long-term social assistance recipients (SA). AE oered a generous wage subsidy that could last up to three years to recipients who found a full-time job within twelve months. The program was implemented on an experimental basis for a single year. Based on little empirical evidence, a slightly modied version of the program was implemented on permanent basis in May 2008. The paper investigates the impact of the temporary program by focusing on the labour market transitions of the targeted population starting one year before the implementation of the program and up until the end of 2005. We use a multi-state multi-episode model. The endogeneity of the participation status is accounted for by treating AE as a distinct state and by allowing correlated unobserved factors to aect the transitions. The model is estimated by the method of simulated moments. Our results show that AE has indeed increased the duration of O-SA spells and decreased the duration of SA spells slightly. There is also some evidence that the response to the program varies considerably with unobserved individual characteristics.Wage subsidy, multi-state multi-episode transition model, social assistance

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.