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

Heavy fermion behavior of itinerant frustrated systems: beta-Mn, Y(Sc)Mn_{2} and LiV_{2}O_{4}$

These three metallic systems do not exhibit any magnetic ordering despite experiments show the existence of localized moments with large antiferromagnetic exchange: this is a consequence of the strong geometric frustration (Y(Sc)Mn_{2} and LiV_{2}O_{4} have the Pyrochlore structure, while beta-Mn has a more complicated frustrated structure). Another common feature is their very large specific heat coefficient \gamma =C/T (420 mJ mole^{-1} K^{-2} for LiV_{2}O_{4}). Several explanations have been proposed for this ''3d heavy fermion behavior'', including a 3d-Kondo effect. However the similarities between the three compounds indicate that frustration plays a big role. We propose a new model which takes into account the existence of two types of 3d-electrons (localized and itinerant) and a frustrated antiferromagnetic exchange between the localized 3d electrons.Comment: Proceedings of HFM-Conference, June 2000, Waterloo, Ontario, Canada To appear in Can. J. Phy

Large amplitude collective dynamic beyond the independent particle/quasiparticle picture

In the present note, a summary of selected aspects of time-dependent mean-field theory is first recalled. This approach is optimized to describe one-body degrees of freedom. A special focus is made on how this microscopic theory can be reduced to a macroscopic dynamic for a selected set of collective variables. Important physical phenomena like adiabaticity/diabaticity, one-body dissipation or memory effect are discussed. Special aspects related to the use of a time-dependent density functional instead of a time-dependent Hartree-Fock theory based on a bare hamiltonian are underlined. The absence of proper description of complex internal correlations however strongly impacts the predictive power of mean-field. A brief overview of theories going beyond the independent particles/quasi-particles theory is given. Then, a special attention is paid for finite fermionic systems at low internal excitation. In that case, quantum fluctuations in collective space that are poorly treated at the mean-field level, are important. Several approaches going beyond mean-field, that are anticipated to improve the description of quantum fluctuations, are discussed: the Balian-V\'en\'eroni variational principle, the Time-Dependent Random Phase Approximation and the recently proposed Stochastic Mean-Field theory. Relations between these theories are underlined as well as their advantages and shortcomings.Comment: To be published in the ebook "Progress of time-dependent nuclear reaction theory" honoring Prof. Joachim Maruhn's retiremen

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

Gender Differences in Parents\u27 Assessment of Language Development

This study aims to determine if there is a statistically significant difference between genders in the reporting of their child’s communication abilities. Possible variances between men and women are important to consider because parent-based questionnaires are often used to help identify children who are in need and eligible for the services of a speech-language pathologist. Literature surrounding parental stereotypes and the impact of the parent in development, as well as stigma in relation to the need for speech therapy services is explored. A survey based off of the Ages and Stages Questionnaire, Third Edition was distributed to parents of children between 24 and 36 months old. While the results of the survey did not show a statistically significant difference between men and women, overarching patterns were found within the data. The most notable trends showed that males consistently reported higher average scores for expressive language-based questions while females reported scores either the same or higher than males for all receptive language-based questions. However, because no statistically difference was found it can be concluded that having only one parent take a questionnaire would not have a large impact on the overall results and subsequent recommendations of a speech-language pathologist

Density Matrix Functional Theory for the Lipkin model

A Density Matrix Functional theory is constructed semi-empirically for the two-level Lipkin model. This theory, based on natural orbitals and occupation numbers, is shown to provide a good description for the ground state energy of the system as the two-body interaction and particle number vary. The application of Density Matrix Functional theory to the Lipkin model illustrates that it could be a valuable tool for systems presenting a shape phase-transition such as nuclei. The improvement of one-body observables description as well as the interest for Energy Density Functional theory are discussed.Comment: 9 pages, 7 figures, to appear in Physical Review

Optimizing stochastic trajectories in exact quantum jump approaches of interacting systems

The quantum jump approach, where pairs of state vectors follow Stochastic Schroedinger Equation (SSE) in order to treat the exact quantum dynamics of two interacting systems, is first described. In this work the non-uniqueness of such stochastic Schroedinger equations is investigated to propose strategies to optimize the stochastic paths and reduce statistical fluctuations. In the proposed method, called the 'adaptative noise method', a specific SSE is obtained for which the noise depends explicitly on both the initial state and on the properties of the interaction Hamiltonian. It is also shown that this method can be further improved by introduction of a mean-field dynamics. The different optimization procedures are illustrated quantitatively in the case of interacting spins. A significant reduction of the statistical fluctuations is obtained. Consequently a much smaller number of trajectories is needed to accurately reproduce the exact dynamics as compared to the SSE without optimization.Comment: 12 pages, 5 figures, revised versio

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

Testing for Zeros in the Spectrum of an Univariate Stationary Process: Part I.

Non parametric and parametric estimation for the spectral density of a stationary process is a well-known topic, except when the spectrum vanishes for some frequency. Indeed, for this frequency, the limit law degenerates, and traditional inference no longer applies. The paper introduces non parametric tests of this hypothesis, which exploit the asymptotic behavior of the periodigram for some well-chosen sequence of frequencies.Stationarity ; Spectral density ; Moving average unit root ; Non parametric tests