  Electromagnetic waves due to electron-positron clouds (bunches), created by
cascading processes in pulsar magnetospheres, have been proposed to explain the
pulsar radio emission. In order to verify this hypothesis, we utilized for the
first time Particle-in-Cell (PIC-) code simulations to study the nonlinear
evolution of electron-positron bunches in dependence on the relative drift
speeds of electrons and positrons, on the initial plasma temperature, and on
the initial distance between the bunches. For this sake, we utilized the
PIC-code ACRONYM with a high-order field solver and particle weighting factor,
appropriate to describe relativistic pair plasmas. We found that the bunch
expansion is mainly determined by the relative electron-positron drift speed.
Finite drift speeds were found to cause the generation of strong electric
fields that reach up to $E \sim 7.5 \times 10^{5}$ V/cm ($E / (m_\mathrm{e} c
\omega_\mathrm{p} e^{-1}) \sim 4.4$) and strong plasma heating. As a result, up
to 15~\% of the initial kinetic energy is transformed into the electric field
energy. Assuming the same electron- and positron-distributions we found that
the fastest (in the bunch reference frame) particles of consecutively emitted
bunches eventually overlap in the momentum (velocity) space. This overlap
causes two-stream instabilities that generate (electrostatic) subluminal L-mode
waves with electric field amplitudes reaching up to $E \sim 1.9\times 10^{4}$
V/cm ($E / (m_\mathrm{e} c \omega_\mathrm{p} e^{-1}) \sim 0.11$). We found that
the interaction of electron-position bunches leads to plasma heating, to the
generation of strong electric fields and of intense superluminal L-mode waves
which, in principle, can be behind the observed electromagnetic emissions of
pulsars in the radio wave range.
