On the Magnetic Field Spectrum and Its Fluctuations in a Primeval Cold Plasma in Thermal Equilibrium

This work reassesses previous results and generalizes the expression for the low-frequency spectrum of magnetic fields fluctuations in a thermal plasma, that was previously obtained within the framework of the fluctuation-dissipation theorem. The new approach presented here is able to avoid any approximation yielding a unique expression that covers both the low- and high-frequency spectrum, without the need of procedures to smooth the junction between the two limit frequency regions formerly used. Also, the simultaneous dependence of this intensity on the plasma and on the collisional frequencies is discussed. Finally, the total emitted plasma energy is compared to the Stefan-Boltzmann law of a pure black-body.