33 research outputs found

    Quark Confinement from Correlation Functions

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    We study quark confinement by computing the Polyakov loop potential in Yang--Mills theory within different non-perturbative functional continuum approaches [1]. We extend previous studies in the formalism of the functional renormalisation group and complement those with findings from Dyson--Schwinger equations and two-particle-irreducible functionals. These methods are formulated in terms of low order Green functions. This allows to identify a criterion for confinement solely in terms of the low-momentum behaviour of correlators.Comment: 8 pages, 3 figures. Talk given at "Xth Quark Confinement and the Hadron Spectrum", Munich, Germany, Oct. 8-12, 201

    Functional renormalisation group in a finite volume

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    We study a Ď•4\phi^4-theory at finite temperature in a finite volume. Quantum, thermal and volume fluctuations are treated with the functional renormalisation group. Specifically, we focus on the interplay of temperature and length scales driving the system. We find that thermodynamical observables at finite volume such as the pressure approach the infinite volume limit similarly to that of the vanishing temperature limit. We also advance the functional renormalisation group method at finite volume. In particular, we identify requirements for suitable regulators that admit the exponential thermal and finite volume decay properties.Comment: 20 pages, 20 figure

    On the Infrared Behavior of Landau Gauge Yang-Mills Theory with a Fundamentally Charged Scalar Field

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    Recently it has been shown that infrared singularities of Landau gauge QCD can confine static quarks via a linearly rising potential. We show that the same mechanism can also provide a confining interaction between charged scalar fields in the fundamental representation. This confirms that within this scenario static confinement is a universal property of the gauge sector even though it is formally represented in the functional equations of the matter sector. The simplifications compared to the fermionic case make the scalar system an ideal laboratory for a detailed analysis of the confinement mechanism in numerical studies of the functional equations as well as in gauge-fixed lattice simulations.Comment: 8 pages, PDFLaTe

    Infrared Behaviour of Landau Gauge Yang-Mills Theory with a Fundamentally Charged Scalar Field

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    The infrared behaviour of the n-point functions of a Yang-Mills theory with a charged scalar field in the fundamental representation of SU(N) is studied in the formalism of Dyson-Schwinger equations. Assuming a stable skeleton expansion solutions in form of power laws for the Green functions are obtained. For a massless scalar field the uniform limit is sufficient to describe the infrared scaling behaviour of vertices. Not taking into account a possible Higgs-phase it turns out that kinematic singularities play an important role for the scaling solutions of massive scalars. On a qualitative level scalar Yang-Mills theory yields similar scaling solutions as recently obtained for QCD.Comment: diploma thesis, submitted May 2009 at the University of Graz (Austria), 73 page

    Gluon spectral functions and transport coefficients in Yang--Mills theory

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    We compute non-perturbative gluon spectral functions at finite temperature in quenched QCD with the maximum entropy method. We also provide a closed loop equation for the spectral function of the energy-momentum tensor in terms of the gluon spectral function. This setup is then used for computing the shear viscosity over entropy ratio η/s\eta/s in a temperature range from about 0.4 Tc0.4\, T_c to 4.5 Tc4.5\, T_c. The ratio η/s\eta /s has a minimum at about 1.25 Tc1.25\, T_c with the value of about 0.115. We also discuss extensions of the present results to QCD.Comment: 5 pages, 4 figure

    On the Infrared Behaviour of Landau Gauge Yang-Mills Theory with Differently Charged Scalar Fields

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    Recently it has been argued that infrared singularities of the quark-gluon vertex of Landau gauge QCD can confine static quarks via a linear potential. It is demonstrated that the same mechanism also may confine fundamental scalar fields. This opens the possibility that within functional approaches static confinement is an universal property of the gauge sector even though it is formally represented in the functional equations of the matter sector. The colour structure of Dyson-Schwinger equations for fundamental and adjoint scalar fields is determined for the gauge groups SU(N) and G(2) exhibiting interesting cancelations purely due to colour algebra.Comment: 3 pages, 1 figure; talk given at the Quark Confinement and the Hadron Spectrum IX, Aug. 30 - Sept. 3, Madrid, Spai

    Phase transitions in dense 2-colour QCD

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    We investigate 2-colour QCD with 2 flavours of Wilson fermion at nonzero temperature T and quark chemical potential mu, with a pion mass of 700 MeV (m_pi/m_rho=0.8). From temperature scans at fixed mu we find that the critical temperature for the superfluid to normal transition depends only very weakly on mu above the onset chemical potential, while the deconfinement crossover temperature is clearly decreasing with mu. We also present results for the Landau-gauge gluon propagator in the hot and dense medium.Comment: 7 pages, 5 figures, talk presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), July 29-August 3 2013, Mainz, German

    Angular distribution of medium-induced QCD cascades

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    We provide a complete description of the angular distribution of gluons in a medium-induced QCD cascade. We identify two components in the distribution, a soft component dominated by soft multiple scatterings, and a hard component dominated by a few hard scatterings. The typical angle that marks the boundary between these two components is determined analytically as a function of the energy of the observed gluon and the size of the medium. We construct the complete solution (beyond the diffusion approximation) in the regime where multiple branchings dominate the dynamics of the cascade in the form of a power series in the number of collisions with the medium particles. The coefficients of this expansions are related to the moments of the distribution in the diffusion approximation and are determined analytically. The angular distribution may be useful in phenomenological studies of jet shapes in heavy-ion collisions.Comment: 20 pages, 3 figure
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