  We study preheating, i.e., non-perturbative resonant decay, of flat direction
fields, concentrating on MSSM flat directions and the right handed sneutrino.
The difference between inflaton preheating and flaton preheating, is that the
potential is more constraint in the latter case. The effects of a complex
driving field, quartic couplings in the potential, and the presence of a
thermal bath are important and cannot be neglected.
  Preheating of MSSM flat directions is typically delayed due to out-of-phase
oscillations of the real and imaginary components and may be preceded by
perturbative decay or $Q$-ball formation. Particle production due to the
violation of adiabaticity is expected to be inefficient due to back reaction
effects. For a small initial sneutrino VEV, $<N > \lesssim m_N/h$ with $m_N$
the mass of the right handed sneutrino and $h$ a yakawa coupling, there are
tachyonic instabilities. The $D$-term quartic couplings do not generate an
effective mass for the tachyonic modes, making it an efficient decay channel.
It is unclear how thermal scattering affects the resonance.
