3,250 research outputs found

    A quantum jump description for the non-Markovian dynamics of the spin-boson model

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    We derive a time-convolutionless master equation for the spin-boson model in the weak coupling limit. The temporarily negative decay rates in the master equation indicate short time memory effects in the dynamics which is explicitly revealed when the dynamics is studied using the non-Markovian jump description. The approach gives new insight into the memory effects influencing the spin dynamics and demonstrates, how for the spin-boson model the the co-operative action of different channels complicates the detection of memory effects in the dynamics.Comment: 9 pages, 6 figures, submitted to Proceedings of CEWQO200

    Thermodynamics of the QCD plasma and the large-N limit

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    The equilibrium thermodynamic properties of the SU(N) plasma at finite temperature are studied non-perturbatively in the large-N limit, via lattice simulations. We present high-precision numerical results for the pressure, trace of the energy-momentum tensor, energy density and entropy density of SU(N) Yang-Mills theories with N=3, 4, 5, 6 and 8 colors, in a temperature range from 0.8T_c to 3.4T_c (where T_c denotes the critical deconfinement temperature). The results, normalized according to the number of gluons, show a very mild dependence on N, supporting the idea that the dynamics of the strongly-interacting QCD plasma could admit a description based on large-N models. We compare our numerical data with general expectations about the thermal behavior of the deconfined gluon plasma and with various theoretical descriptions, including, in particular, the improved holographic QCD model recently proposed by Kiritsis and collaborators. We also comment on the relevance of an AdS/CFT description for the QCD plasma in a phenomenologically interesting temperature range where the system, while still strongly-coupled, approaches a `quasi-conformal' regime characterized by approximate scale invariance. Finally, we perform an extrapolation of our results to the N to ∞\infty limit.Comment: 1+38 pages, 13 eps figures; v2: added reference

    Determination of the ΔS=1\Delta S = 1 weak Hamiltonian in the SU(4) chiral limit through topological zero-mode wave functions

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    A new method to determine the low-energy couplings of the ΔS=1\Delta S=1 weak Hamiltonian is presented. It relies on a matching of the topological poles in 1/m21/m^2 of three-point correlators of two pseudoscalar densities and a four-fermion operator, measured in lattice QCD, to the same observables computed in the ϵ\epsilon-regime of chiral perturbation theory. We test this method in a theory with a light charm quark, i.e. with an SU(4) flavour symmetry. Quenched numerical measurements are performed in a 2 fm box, and chiral perturbation theory predictions are worked out up to next-to-leading order. The matching of the two sides allows to determine the weak low-energy couplings in the SU(4) limit. We compare the results with a previous determination, based on three-point correlators containing two left-handed currents, and discuss the merits and drawbacks of the two procedures.Comment: 38 pages, 9 figure

    Weak low-energy couplings from topological zero-mode wavefunctions

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    We discuss a new method to determine the low-energy couplings of the ΔS=1\Delta S=1 weak Hamiltonian in the ϵ\epsilon-regime. It relies on a matching of the topological poles in 1/m21/m^2 of three-point functions of two pseudoscalar densities and a four-fermion operator computed in lattice QCD, to the same observables in the Chiral Effective Theory. We present the results of a NLO computation in chiral perturbation theory of these correlation functions together with some preliminary numerical results.Comment: 7 pages. Contribution to Lattice 200

    Helical Magnetic Fields from Inflation

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    We analyze the generation of seed magnetic fields during de Sitter inflation considering a non-invariant conformal term in the electromagnetic Lagrangian of the form −14I(ϕ)FμνF~μν-\frac14 I(\phi) F_{\mu \nu} \widetilde{F}^{\mu \nu}, where I(ϕ)I(\phi) is a pseudoscalar function of a non-trivial background field ϕ\phi. In particular, we consider a toy model, that could be realized owing to the coupling between the photon and either a (tachyonic) massive pseudoscalar field and a massless pseudoscalar field non-minimally coupled to gravity, where II follows a simple power-law behavior I(k,η)=g/(−kη)βI(k,\eta) = g/(-k\eta)^{\beta} during inflation, while it is negligibly small subsequently. Here, gg is a positive dimensionless constant, kk the wavenumber, η\eta the conformal time, and β\beta a real positive number. We find that only when β=1\beta = 1 and 0.1≲g≲20.1 \lesssim g \lesssim 2 astrophysically interesting fields can be produced as excitation of the vacuum, and that they are maximally helical.Comment: 17 pages, 1 figure, subsection IIc and references added; accepted for publication in IJMP

    Real-time static potential in hot QCD

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    We derive a static potential for a heavy quark-antiquark pair propagating in Minkowski time at finite temperature, by defining a suitable gauge-invariant Green's function and computing it to first non-trivial order in Hard Thermal Loop resummed perturbation theory. The resulting Debye-screened potential could be used in models that attempt to describe the ``melting'' of heavy quarkonium at high temperatures. We show, in particular, that the potential develops an imaginary part, implying that thermal effects generate a finite width for the quarkonium peak in the dilepton production rate. For quarkonium with a very heavy constituent mass M, the width can be ignored for T \lsim g^2 M/12\pi, where g^2 is the strong gauge coupling; for a physical case like bottomonium, it could become important at temperatures as low as 250 MeV. Finally, we point out that the physics related to the finite width originates from the Landau-damping of low-frequency gauge fields, and could be studied non-perturbatively by making use of the classical approximation.Comment: 20 pages. v2: a number of clarifications and a few references added; published versio

    Remote polarization entanglement generation by local dephasing and frequency upconversion

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    We introduce a scheme for remote entanglement generation for the photon polarization. The technique is based on transferring the initial frequency correlations to specific polarization-frequency correlations by local dephasing and their subsequent removal by frequency up-conversion. On fundamental level, our theoretical results show how to create and transfer entanglement, to particles which never interact, by means of local operations. This possibility stems from the multi-path interference and its control in frequency space. For applications, the developed techniques and results allow for the remote generation of entanglement with distant parties without Bell state measurements and opens the perspective to probe frequency-frequency entanglement by measuring the polarization state of the photons.Comment: 8 page
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