Lerche, Christophvon Smekal, Lorenz Johann Maria2007-07-052007-07-052002Physical Review D, 2002; 65(12):1250061550-7998http://hdl.handle.net/2440/34444In the covariant description of confinement, one expects the ghost correlations to be infrared enhanced. Assuming ghost dominance, the long-range behavior of gluon and ghost correlations in Landau gauge QCD is determined by one exponent κ. The gluon propagator is infrared finite (vanishing) for κ=1/2 (κ>1/2) which is still under debate. Here, we study the critical exponent and coupling for the infrared conformal behavior from the asymptotic form of the solutions to the Dyson-Schwinger equations in an ultraviolet finite expansion scheme. The value for κ is directly related to the ghost-gluon vertex. Assuming that it is regular in the infrared, one obtains κ≃0.595. This value maximizes the critical coupling αc(κ), yielding αcmax≃(4π/Nc)0.709≈2.97 for Nc=3. For larger κ the vertex acquires an infrared singularity in the gluon momentum; smaller ones imply infrared singular ghost legs. Variations in αc remain within 5% from κ=0.5 to 0.7. Above this range, αc decreases more rapidly with αc→0+ as κ⃗1- which sets the upper bound on κ.en©2002 American Physical SocietyJournal article002006349610.1103/PhysRevD.65.1250062-s2.0-0037098354