61 research outputs found

    Monte Carlo Hamiltonian

    Get PDF
    We suggest how to construct an effective low energy Hamiltonian via Monte Carlo starting from a given action. We test it by computing thermodynamical observables like average energy and specific heat for simple quantum systems.Comment: Contribution to Lattice'99 (Theoretical developments) Text (LaTeX file) + 2 figures (ps files

    Renormalisation in Quantum Mechanics

    Get PDF
    We study a recently proposed quantum action depending on temperature. We construct a renormalisation group equation describing the flow of action parameters with temperature. At zero temperature the quantum action is obtained analytically and is found free of higher time derivatives. It makes the quantum action an ideal tool to investigate quantum chaos and quantum instantons.Comment: replaced version with new figs. Text (LaTeX), 3 Figs. (ps

    Proximity effect in multiterminal hybrid structures

    Full text link
    We consider the proximity effect in multiterminal ferromagnet superconductor (FSF) hybrid structures in which two or three electrodes are connected to a superconductor. We show that two competing effects take place in these systems: (i) pair breaking effects due to the response to the exchange field induced in the superconductor; (ii) a reduction of the \SOP at the interface that takes place already in NS junctions. We focus on this second effect that dominates if the thickness of the S layer is small enough. We consider several single-channel electrodes connected to the same site. We calculate the superconducting order parameter and the local density of state (LDOS). With two ferromagnetic electrodes connected to a superconductor we find that the superconducting order parameter in the ferromagnetic alignment is larger than the superconducting order parameter in the antiferromagnetic alignment (ΔF>ΔAF\Delta_{\rm F} >\Delta_{\rm AF}), in agreement with [Eur. Phys. J. B {\bf 25}, 373 (2002)]. If a third spin polarized electrode is connected to a superconductor we find that ΔF−ΔAF\Delta_{\rm F}-\Delta_{\rm AF} can change sign as the transparency of the third electrode increases. This can be understood from the fact that the superconducting order parameter is reduced if pair correlations among the ferromagnetic electrodes increase. If the two ferromagnetic electrodes are within a finite distance we find Friedel oscillations in the Gorkov function but we still obtain ΔF>ΔAF\Delta_{\rm F} > \Delta_{\rm AF}.Comment: 21 pages, 17 figure

    Five-Dimensional BF Theory and Four-Dimensional Current Algebra

    Get PDF
    We consider the relation between the five-dimensional BF model and a four-dimensional local current algebra from the point of view of perturbative local quantum field theory. We use an axial gauge fixing procedure and show that it allows for a well defined theory which actually can be solved exactly.Comment: 15 pages LaTeX file +3 Figures in TexDraw (available from hep-th) LATEX-compatibility Bug fixe

    Test of Quantum Action for Inverse Square Potential

    Get PDF
    We present a numerical study of the quantum action previously introduced as a parametrisation of Q.M. transition amplitudes. We address the questions: Is the quantum action possibly an exact parametrisation in the whole range of transition times (0<T<∞0 < T < \infty)? Is the presence of potential terms beyond those occuring in the classical potential required? What is the error of the parametrisation estimated from the numerical fit? How about convergence and stability of the fitting method (dependence on grid points, resolution, initial conditions, internal precision etc.)? Further we compare two methods of numerical determination of the quantum action: (i) global fit of the Q.M. transition amplitudes and (ii) flow equation. As model we consider the inverse square potential, for which the Q.M. transition amplitudes are analytically known. We find that the relative error of the parametrisation starts from zero at T=0 increases to about 10−310^{-3} at T=1/EgrT=1/E_{gr} and then decreases to zero when T→∞T \to \infty. Second, we observe stability of the quantum action under variation of the control parameters. Finally, the flow equation method works well in the regime of large TT giving stable results under variation of initial data and consistent with the global fit method.Comment: Text (LaTeX), Figures(ps

    Algorithm for Computing Excited States in Quantum Theory

    Full text link
    Monte Carlo techniques have been widely employed in statistical physics as well as in quantum theory in the Lagrangian formulation. However, in the conventional approach, it is extremely difficult to compute the excited states. Here we present a different algorithm: the Monte Carlo Hamiltonian method, designed to overcome the difficulties of the conventional approach. As a new example, application to the Klein-Gordon field theory is shown.Comment: 3 pages, uses Latex and aipproc.cl

    The identity of destruction and the construction of identity in L’amour la fantasia of Assia Djebar and Une odeur de mantùque of Mohammed Khair-Eddine

    Full text link
    Francophone diaspora literature reveals unstable worlds. In facts, the metamorphosis of the self would be a reflection of a number of unconventional narrative forms: reflexive territories whose benchmarks would be, mainly, at the level of migratory movements. Such a broad subject could be partially identified on the basis of a definite corpus. Two authors draw attention to this: Assia Djebar and Mohammed KhaĂŻr-Eddine. Their respective works, L\u27Amour la fantasia and Une Odeur de mantĂšque, lead the recipient to a rather intriguing journey insofar as memory, enunciation and temporality intersect with the fields of otherness and de-territoriality. By means of a comparative approach, we propose a modest illumination on these inner-self and outer-self problematized spaces. Weighing with all their strenght on postmodernity, they still resonate in the 21st century with the critical margins of the collective unconscious

    Quantum Chaos at Finite Temperature

    Get PDF
    We use the quantum action to study quantum chaos at finite temperature. We present a numerical study of a classically chaotic 2-D Hamiltonian system - harmonic oscillators with anharmonic coupling. We construct the quantum action non-perturbatively and find temperature dependent quantum corrections in the action parameters. We compare Poincar\'{e} sections of the quantum action at finite temperature with those of the classical action.Comment: Text (LaTeX), Figs. (ps