2-COMPONENT COSMOLOGICAL PLASMAS

We generalize our previous work to perform a detailed study of the mod es of a two-component cosmological plasma. We are interested in the an alytical form of modes not obtainable by our one-component and magneto hydrodynamical treatments, for example, ion-sound modes. These types o f modes may be found in an electron-proton plasma, both in the radiati on-dominated era and in the post-recombination era. We use the fluid e quations previously derived in the nonrelativistic limit, with an exte rnal background magnetic field. We search for modes both with the fiel d neglected and explicitly contained, but pay more attention to the fi eld-free modes in this paper. The ion mass corrections to Langmuir mod es are obtained, and the new ion-sound mode is studied in detail. Part icular attention is paid to deriving an analytical form for the pertur bed number densities and obtaining the redshifted observable frequenci es from this. The differences in redshift of the various quantities th at enter in constructing the modes, depending on whether the dynamics is dominated by matter or radiation, are illustrated. We also briefly explore the two-component transverse mode. As a prelude to possible fu rther work, we derive the equations for longitudinal magnetoplasma mod es and indicate the expected outcome for the solutions. Finally we pre sent a general analytical method for finding leading asymptotic forms for any mode covered by our formalism. [S0556-2821(97)01124-7].