Coherent emission mechanisms in radio pulsars

In this work we investigate some possible mechanisms for pulsar radio emission. First we analyze the normal modes of a strongly magnetized electron-positron plasma taking into account a possible difference in the distribution functions of electrons and positrons. The dispersion relations, polarization properties and various regimes of beam instabilities in pair plasma are considered. We argue that kinetic instabilities of electromagnetic modes are more promising candidates for the pulsar radio emission mechanism than electrostatic instabilities (which occur in the hydrodynamic regime). We elucidate the microphysical processes underlying cyclotron-Cherenkov and Cherenkov-drift emission, stressing the importance of collective plasma effects involving all the particles of a medium. We show that cyclotron-Cherenkov emission at the anomalous Doppler effect can account for various observed phenomena of the "core" emission. Cherenkov-drift emission is a likely candidate for the "cone" emission. We developed a new description that treats Cherenkov-drift emission in cylindrical coordinates. This approach describes consistently the resonant wave-particle interaction and provides a link between the Cherenkov, curvature and drift emission mechanisms recovering them as a limiting cases of the Cherenkov-drift emission process. We also consider two possible nonlinear stages of the development of the cyclotron-Cherenkov instability: quasilinear diffusion and induced Raman scattering. We calculate the asymptotic particle distribution and emerging spectra for the cyclotron-Cherenkov instability and also show that induced Raman scattering may be important for the wave propagation and nonlinear saturation of electromagnetic instabilities. Finally, we considered the escape of waves from a pulsar magnetosphere taking into account cyclotron, Cherenkov and Cherenkov-drift absorption processes