Emergence of new quasiparticles in quantum electrodynamics at finite temperature

We study the spectrum of fermionic excitations in a hot relativistic electron plasma. Numerical analysis of the one-loop electron propagator shows the appearance of new quasiparticle modes, as already studied in the massless fermion limit, as the temperature is raised to exceed the electron mass m. We calculate the relevant spectral densities and show that one mode, whose splitting in energy from the original electron is of the order of m, moves as the temperature is raised towards higher frequency along with the electron while retaining a narrow width. We compare results derived in Feynman and Coulomb gauges. The role of the zero-temperature counterterms is discussed.