The contribution of thermal electron-positron pairs to the thermodynamic properties of black-body radiation

Abstract

The contribution of thermal electron-positron pairs to the thermodynamic properties of black-body radiation (BBR) is considered. This contribution is examined in the vicinity of the temperature corresponding to the electron rest mass energy Tc=mcc2/ kappa , in which it becomes appreciable. The correction factors are defined as the ratio of extended thermodynamic expressions of BBR (which also include the contributions from thermal pairs) to the familiar expressions of it. Then the variation of these factors with temperature is given. It is shown that while they have the same value for each property in both high and low temperature regimes (T>>Tc and T<<Tc), they have different values about 0.5 Tc. It is found that for BBR, the ratio of the energy density to the pressure has a maximum about 0.33 Tc and also the ratio of the specific heats has a minimum about 0.4 Tc.