Infrared features of unquenched finite temperature lattice Landau gauge QCD

Abstract

The color diagonal and color antisymmetric ghost propagators slightly above Tc of N f = 2 MILC 24 3 × 12 lattices are measured and compared with zero temperature unquenched N f = 2 + 1 MILCc 20 3 × 64 and MILC f 28 3 × 96 lattices and zero temperature quenched 56 4 β = 6.4 and 6.45 lattices. The expectation value of the color antisymmetric ghost propagator φ c (q) is zero but its Binder cumulant, which is consistent with that of N 2 c − 1 dimensional Gaussian distribution below Tc, decreases above Tc. Although the color diagonal ghost propagator is temperature independent, the l 1 norm of the color antisymmetric ghost propagator is temperature dependent. The expectation value of the ghost condensate observed at zero temperature unquenched configuration is consistent with 0 in T > Tc.We also measure transverse, magnetic and electric gluon propagator and extract gluon screening masses. The running coupling measured from the product of the gluon dressing function and the ghost dressing function are almost temperature independent but the effect of A 2 condensate observed at zero temperature is consistent with 0 in T > Tc.The transverse gluon dressing function at low temperature has a peak in the infrared at low temperature but it becomes flatter at high temperature. The magnetic gluon propagator at high momentum depends on the temperature. These data imply that the magnetic gluon propagator and the color antisymmetric ghost propagator are affected by the presence of dynamical quarks and there are strong non-perturbative effects through the temperature-dependent color anti-symmetric ghost propagator.

QCD effective charges from lattice data

“…The KugoOjima function has been simulated on the lattice by means of Monte-Carlo averages of the operator time-ordered product appearing on the left-hand side of the defining equation (2.15) [69][70][71][72]. Given that G(q 2 ) = u(q 2 ), the lattice information on u(q 2 ) may be used, in principle, into (2.14), together with the lattice results for the Landau gauge ∆(q 2 ).…”

“…As already mentioned in the previous section, G(q 2 ) in the Landau gauge coincides with the KO function, usually denoted in the literature by u(q 2 ). This function has been computed on the lattice in the early work of [69][70][71] and more recently in [72], mainly motivated by its relation with the well-known Kugo-Ojima confinement criterion. These lattice studies established clearly that the aforementioned criterion is not satisfied, since u(0) ≈ 0.6 deviates appreciably from the special value of −1.…”

AdS/CFT and Light-Front QCD

“…For higher spin bosonic modes we can also recast the wave equation AdS (12) into its light-front form (13). Using the substitution φ S (ζ) = ζ −3/2+S Φ S (ζ), ζ = z, we find a LF Schrödinger equation identical to (14) with φ → φ S , provided that (µR)…”

“…Solutions of the Dyson-Schwinger equations for the three-gluon and four-gluon couplings [1,2,3,4,5,6,7] and phenomenological studies [8,9,10] of QCD couplings based on physical observables such as τ decay [11] and the Bjorken sum rule [12], show that the QCD β function vanishes and α s (Q 2 ) become constant at small virtuality; i.e., effective charges develop an "infrared fixed point." Recent lattice simulations [13,14] and nonperturbative analyses [15] have also indicated an infrared fixed point for QCD. One can understand this physically [16]: in a confining theory where gluons have an effective mass [17] or maximal wavelength, all vacuum polarization corrections to the gluon self-energy decouple at long wavelength; thus an infrared fixed point appears to be a natural consequence of confinement.…”

Higher-twist effects in the direct photon production and the role of infrared renormalons

“…AdS/CFT duality also gives accurate predictions for hadron spectroscopy, and a description of the quark structure of hadrons which has scale invariance, dimensional counting at short distances, and color confinement at large distances [1][2][3][4][5][6][7][8]. Based on AdS/CFT correspondence, where there have been many significant theoretical advances using this theory as application, interesting and important attempts have been made to understand the nonperturbative aspects of QCD under the name ''holographic QCD.''…”