28,468 research outputs found

    Cumulant Expansions and the Spin-Boson Problem

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    The dynamics of the dissipative two-level system at zero temperature is studied using three different cumulant expansion techniques. The relative merits and drawbacks of each technique are discussed. It is found that a new technique, the non-crossing cumulant expansion, appears to embody the virtues of the more standard cumulant methods.Comment: 26 pages, LaTe

    Critical Binder cumulant of two-dimensional Ising models

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    The fourth-order cumulant of the magnetization, the Binder cumulant, is determined at the phase transition of Ising models on square and triangular lattices, using Monte Carlo techniques. Its value at criticality depends sensitively on boundary conditions, details of the clusters used in calculating the cumulant, and symmetry of the interactions or, here, lattice structure. Possibilities to identify generic critical cumulants are discussed.Comment: 6 pages, 4 figures, submitted to Eur. Phys. J.

    High-order current correlation functions in Kondo systems

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    We examine the statistics of current fluctuations in a junction with a quantum dot described by Kondo Hamiltonian. With the help of modified Keldish technique we calculate the third current cumulant. As a function of ratio v=eV/TKv=eV/T_{K} the 3rd cumulant was obtained for three different regimes: Fermi liquid regime (v>1). Unlike the case of noninteracting dot, 3rd cumulant shows strong non-linear voltage dependence. Only in the asymptotical limit of large voltages the linear dependence on VV is recovered.Comment: 5 pages, 2 figure