ONE-PARTICLE AND COLLECTIVE ELECTRON-SPECTRA IN HOT AND DENSE QED ANDTHEIR GAUGE DEPENDENCE

The one-particle electron spectrum is found for hot and dense QED and its properties are investigated in comparison with the collective spec trum. It is shown that the one-particle spectrum (in any case its sere momentum limit) is gauge-invariant, but the collective spectrum, bein g qualitatively different, is always gauge-dependent. The exception is the case m,mu = 0 for which the collective spectrum long wavelength l imit demonstrates the gauge invariance as well.