Physical Processes in Relativistic Plasmas.

Physical processes occurring in semirelativistic and relativistic plasmas are studied and their influence on the equilibrium properties of thermal plasmas is determined. In Part I the pair annihilation process is considered in detail. Exact analytical expressions are derived in the Born approximation for the pair annihilation rate and spectral emissivity from isotropic, monoenergetic electrons and positrons of arbitrary energies. The annihilation rate and spectral emissivity for arbitrary particle distribution functions are given as double integrals. Asymptotic expressions are derived for the annihilation rate, the cooling rate, and the spectral emissivity at relativistic temperatures. Useful, approximate expressions, valid at temperatures larger than 10('8)K, are given for the annihilation rate and the cooling rate. In Part II the physical properties of a thermal plasma in the temperature range (theta) (= kT/mc('2), where m is the electron mass) = 1/3 - 100 are studied assuming pair equilibrium and thermal balance. All important pair and photon producing processes in a plasma with a Thomson scattering optical depth (tau)(,T) of order unity or less are included. The spectral emissivities and the cooling rates for bremsstrahlung and pair annihilation are discussed. The pair production rates and the pair annihilation rate as well as the opacities are calculated. Simple approximate expressions are given for several rates. The equilibrium ratio z of the pair density to the proton density N is given by the roots to the pair equilibrium equation (a polynomial in z). For a given (tau)(,N) = Nr(,e)('2)R < 10('-1) there exists a temperature (theta)(,c) beyond which the pair annihilation rate cannot balance the pair production rate and there are no pair equilibria. For (theta) < (theta)(,c) there are a high -z pair equilibrium branch (z >> 1), where photon-photon pair production dominates, and a low-z pair equilibrium branch (z << (tau)(,N)('-1)), where particle-particle pair production dominates. The temperature (theta)(,c) has a maximum value (theta)(,max) (TURNEQ) 25 for (tau)(,N) < 10('-3) and decreases monotonically for larger (tau)(,N). Several aspects of the obtained pair equilibria, such as parameter space dependence, cooling rates, optical depths, stability and confinement are briefly discussed.