THE STRONG PHASE OF QED

The strong phase of QED is studied in the ladder approximation. In the leading approximation we show that the perturbative vacuum of QED is unstable against forming the electron-positron bound state if the coupling is greater than a critical value. We argue that the chiral symmetry is spontaneously broken in the strong phase of QED, if we choose the correct boundary conditions to the gap equation and the nonperturbative β-function found by Miransky is taken into account. We also calculate the ratio between the infrared limit of the electron self-energy and the vacuum condensate, γ = Σ2(0)/k = 1. © 1990.