Debye mass squared are shown as functions of the energy $\omega$ scaled by the momentum $k$ which is fixed at $k=0.5T$. \[fig:gluon se\]](PiLGraph2.eps "fig:")

![The real and imaginary parts of the retarded quark self-energies for the normal (left) and abnormal branch (right) scaled by the plasma frequency squared are shown as functions of the energy $\omega$ scaled by the momentum $k$ which is fixed at $k=0.5T$. \[fig:quark se\]](SigmaPlusGraph2.eps "fig:")        ![The real and imaginary parts of the retarded quark self-energies for the normal (left) and abnormal branch (right) scaled by the plasma frequency squared are shown as functions of the energy $\omega$ scaled by the momentum $k$ which is fixed at $k=0.5T$. \[fig:quark se\]](SigmaMinusGraph2.eps "fig:")

It follows directly from eqs. (\[eq:Im PiT\])-(\[eq:Im Sigmapm\]) that the HTL self-energies do not account for quasiparticle widths since the imaginary parts are zero at the poles of the quasiparticle propagators, i.e. above the light cone. The nonzero imaginary parts of the self-energies below the light cone are due to *Landau damping* (LD). LD is a collective effect caused by energy transfer between the gauge field and plasma particles with velocities close to the phase velocity (“resonant particles”).

Even though the imaginary parts are formally nonzero 