The Spectrum of QED₁₊₁ in the framework of the DLCQ method

We investigate the influence of the fermion field boundary conditions on the spectrum and wavefunctions of QED$_{1+1}$ in the Discretized Light-Cone Quantization formalism suggested by Pauli and Brodsky. The basic lesson is that one Fourier mode (namely the zero mode) can be decisive for even the ground state mass. The choice of boundary conditions is seen to be not important, if and only if all degrees of freedom are treated properly. This is still a problem for light-cone quantization in general.