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The Infrared Behavior of Gluon, Ghost, and Quark Propagators in Landau Gauge QCD

A truncation scheme for the Dyson-Schwinger equations of QCD in Landau gauge is presented which implements the Slavnov-Taylor identities for the 3-point vertex functions. Neglecting contributions from 4-point correlations such as the 4-gluon vertex function and irreducible scattering kernels, a closed system of equations for the propagators is obtained. For the pure gauge theory without quarks this system of equations for the propagators of gluons and ghosts is solved in an approximation which allows for an analytic discussion of its solutions in the infrared: The gluon propagator is shown to vanish for small spacelike momenta whereas the ghost propagator is found to be infrared enhanced. The running coupling of the non-perturbative subtraction scheme approaches an infrared stable fixed point at a critical value of the coupling, $α_c \simeq 9.5$. The gluon propagator is shown to have no Lehmann representation. The gluon and ghost propagators obtained here compare favorably with recent lattice calculations. Results for the quark propagator in the quenched approximation are presented.