  Imposing initial conditions to nonequilibrium systems at some time t_0 leads,
in renormalized quantum field theory, to the appearance of singularities in the
variable t-t_0 in relevant physical quantities, such as energy density and
pressure. The origin of these `initial singularities' can be traced back to the
choice of initial state. We construct here, by a Bogoliubov transformation,
initial states such that these singularities are eliminated. While the
construction is not unique it can be considered a minimal way of taking into
account the nonequilibrium evolution of the system prior to t_0.
