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

Symmetry as a source of hidden coherent structures in quantum physics: general outlook and examples

A general algebraic approach, incorporating both invariance groups and dynamic symmetry algebras, is developed to reveal hidden coherent structures (closed complexes and configurations) in quantum many-body physics models due to symmetries of their Hamiltonians $H$. Its general ideas are manifested on some recent new examples: 1) G-invariant bi-photons and a related SU(2)-invariant treatment of unpolarized light; 2) quasi-spin clusters in nonlinear models of quantum optics; 3) construction of composite particles and (para)fields from G-invariant clusters due to internal symmetries.Comment: 10 pages, LATEX; Proceedings of VIII Int. Conf. on Symmetry Methods in Physics (Dubna, July 28-August 2, 1997

Stochastic quantum dynamics beyond mean-field

Mean-field approaches where a complex fermionic many-body problem is replaced by an ensemble of independent particles in a self-consistent mean-field can describe many static and dynamical aspects. It generally provides a rather good approximation for the average properties of one-body degrees of freedom. However, the mean-field approximation generally fails to produce quantum fluctuations of collective motion. To overcome this difficulty, noise can be added to the mean-field theory leading to a stochastic description of the many-body problem. In the present work, we summarize recent progress in this field and discuss approaches where fluctuations have been added either to the initial time, like in the Stochastic Mean-Field theory or continuously in time as in the Stochastic Time-Dependent Hartree-Fock. In some cases, the initial problem can even be re-formulated exactly by introducing Quantum Monte-Carlo methods in real-time. The possibility to describe superfluid systems is also invoked. Successes and shortcomings of the different beyond mean-field theories are discussed and illustrated.Comment: 34 pages, submitted to EPJA-Review sectio

The collective quantization of three-flavored Skyrmions revisited

A self-consistent large $N_c$ approach is developed for the collective quantization of SU(3) flavor hedgehog solitons, such as the Skyrmion. The key to this analysis is the determination of all of the zero modes associated with small fluctuations around the hedgehog. These are used in the conventional way to construct collective coordinates. This approach differs from previous work in that it does not implicitly assume that each static zero mode is associated with a dynamical zero mode. It is demonstrated explicitly in the context of the Skyrmion that there are fewer dynamical zero modes than static ones due to the Witten-Wess-Zumino term in the action. Group-theoretic methods are employed to identify the physical states resulting from canonical quantization of the collectively rotating soliton. The collective states fall into representations of SU(3) flavor labeled by $(p,q)$ and are given by $(2J, \frac{Nc}{2} -J)$ where $J={1/2},{3/2},...$ is the spin of the collective state. States with strangeness $S > 0$ do not arise as collective states from this procedure; thus the $\theta^{+}$ (pentaquark) resonance does not arise as a collective excitation in models of this type.Comment: 12 pages; uses package "youngtab

Mobile impurities in integrable models

We use a mobile impurity or depleton model to study elementary excitations in one-dimensional integrable systems. For Lieb-Liniger and bosonic Yang-Gaudin models we express two phenomenological parameters characterising renormalised inter- actions of mobile impurities with superfluid background: the number of depleted particles, $N$ and the superfluid phase drop $\pi J$ in terms of the corresponding Bethe Ansatz solution and demonstrate, in the leading order, the absence of two-phonon scattering resulting in vanishing rates of inelastic processes such as viscosity experienced by the mobile impuritiesComment: 25 pages, minor corrections made to the manuscrip

Innovation brokers and their roles in value chain-network innovation: preliminary findings and a research agenda

Intervention approaches have been implemented in developing countries to enhance farmer's livelihoods through improving their linkages to markets and inclusiveness in agricultural value chains. Such interventions are aimed at facilitating the inclusion of small farmers not just in the vertical activities of the value chain (coordination of the chain) but also in the horizontal activities (cooperation in the chain). Therefore value addition is made by not just innovating products and services, but also by innovating social processes, which we define as Value Chain-Network Innovation. In Value Chain-Network Innovation, linkage formation among networks and optimisation is one of the main objectives of innovation enhancing interventions. Here some important roles for innovation brokers are envisaged as crucial to dynamise this process, connecting different actors of the innovation system, paying special attention to the weaker ones. However, little attention has been given to identify different innovation brokering roles in those approaches, and to the need that they facilitate innovation processes and open safe spaces for innovation and social learning at different organisational settings and levels, to have more effective and sustainable impacts. This paper offers some preliminary empirical evidence of the roles of innovation brokers in a developing country setting, recognising the context-sensitive nature of innovations. Two cases from work experience with intervention approaches are analysed in light of the theories of innovation brokering, presenting some empirical evidence of different types of arrangements made by innovation brokers. A third case was taken from the literature. Data from questionnaires, key informant interviews, participant observations of different types of activities and processes carried out in those approaches, SWOT analysis and project reports were used for the analysis of different types of brokering roles and to draw some lessons. One important outcome of this preliminary analysis was that Information and Communication Technologies (ICT) in integration with other media facilitate new ways of social organisation and interaction of innovation networks, which offer more possibilities for processes of innovation, aggregating value to the production and sharing of knowledge. There is already a transition of paradigm for approaching agricultural innovation to more participative and open approaches, which offers a promissory landscape for organising the value chain actors in a way that is more favourable for small farmers

Resist, comply or workaround? An examination of different facets of user engagement with information systems

This paper provides a summary of studies of user resistance to Information Technology (IT) and identifies workaround activity as an understudied and distinct, but related, phenomenon. Previous categorizations of resistance have largely failed to address the relationships between the motivations for divergences from procedure and the associated workaround activity. This paper develops a composite model of resistance/workaround derived from two case study sites. We find four key antecedent conditions derived from both positive and negative resistance rationales and identify associations and links to various resultant workaround behaviours and provide supporting Chains of Evidence from two case studies

Field Theoretic Formulation of Kinetic theory: I. Basic Development

We show how kinetic theory, the statistics of classical particles obeying Newtonian dynamics, can be formulated as a field theory. The field theory can be organized to produce a self-consistent perturbation theory expansion in an effective interaction potential. The need for a self-consistent approach is suggested by our interest in investigating ergodic-nonergodic transitions in dense fluids. The formal structure we develop has been implemented in detail for the simpler case of Smoluchowski dynamics. One aspect of the approach is the identification of a core problem spanned by the variables \rho the number density and B a response density. In this paper we set up the perturbation theory expansion with explicit development at zeroth and first order. We also determine all of the cumulants in the noninteracting limit among the core variables \rho and B.Comment: 45 page