Dispersion relation of EF waves calculated from linear theory. The frequency ω_r (solid curve) and growth rate γ (dashed curve) of the EF waves are shown normalized to the proton gyrofrequency as a function of parallel wavenumber k_∥ normalized to the inertial length of the protons. The plasma parameters are ﹩T^{e}_{\parallel }/ T^{e}_{\perp }=15﹩, ﹩T^{p}_{\parallel }/ T^{p}_{\perp }=2﹩, ﹩T^{e}_{\perp }=T^{p}_{\perp }=1\times 10^{7}﹩ K, ﹩n_{e}=n_{p}=5\times 10^{10}﹩ cm⁻³, and ﹩B_{0}=100﹩ G. The sign convention is that ﹩k> 0﹩ and ﹩\omega > 0﹩ mean left‐hand circularly polarized; ﹩\gamma > 0﹩ refers to growing modes. The dotted horizontal lines indicate the gyrofrequency of the corresponding ion species.