  The study of the evolution of a suprathermal electron beam traveling through
a background plasma is relevant for the physics of solar flares and their
associated type III solar radio bursts. As they evolve guided by the coronal
magnetic field-lines, these beams generate Langmuir turbulence. The
beam-generated turbulence is in turn responsible for the emission of radio
photons at the second harmonic of the local plasma frequency, which are
observed during type III solar radio bursts. To generate the radio emission,
the beam-aligned Langmuir waves must coalesce, and therefore a process capable
of re-directioning the turbulence in an effective fashion is required.
  Different theoretical models identify the electrostatic (ES) decay process L1
-> L2 + S (L: Langmuir wave; S: Ion-acoustic wave) as the re-directioning
mechanism for the L waves. Two different regimes have been proposed to play a
key role: the back-scattering and the diffusive (small angle) scattering. This
paper is a comparative analysis of the decay rate of the ES decay for each
regime, and of the different observable characteristics that are expected for
the resulting ion-acoustic waves.
