  By identifying a norm capturing the effect of the forcing governed by the
Poisson equation, we give a detailed spectrum analysis on the linearized
Vlasov-Poisson-Boltzmann system around a global Maxwellian. It is shown that
the electric field governed by the self-consistent Poisson equation plays a key
role in the analysis so that the spectrum structure is genuinely different from
the well-known one of the Boltzmann equation. Based on this, we give the
optimal time decay rates of solutions to the equilibrium.
