Landau gauge peculiarity in QED Schwinger-Dyson equation

Spontaneous chiral symmetry breaking solutions for the Schwinger-Dyson equation in massless QED are investigated in the covariant α-gauge. With a proper renormalization of the mass function Σ, critical solutions Σc are obtained along the whole criticality on the λ-α plane (λ=3e2/4π). For positive α, Σc(x) is a momentum independent constant function. The renormalization flow and fixed point structure on the λ-α plane is clarified. The Landau gauge critical point (λ=1, α=0) shows up as an ultraviolet fixed point with two relevant operators. (author)