Boltzmann equations for preheating
  We derive quantum Boltzmann equations for preheating by means of the density
matrix formalism, which account for both the non-adiabatic particle production
and the leading collisional processes between the produced particles. In so
doing, we illustrate the pivotal role played by pair correlations in mediating
the particle production. In addition, by numerically solving the relevant
system of Boltzmann equations, we demonstrate that collisional processes lead
to a suppression of the growth of the number density even at the very early
stages of preheating.
