  Considering quantum cosmological minisuperspace models with positive
potential, we present evidence that
  (i) despite common belief there are perspectives for defining a unique,
naturally preferred decomposition of the space H of wave functions into two
subspaces H^\pm that generalizes the concept of positive and negative
frequency, and that
  (ii) an underlying unitary evolution within these two subspaces exists and
may be described in analogy to the representation of a geometric object in
local coordinates: it is associated with the choice of a congruence of
classical trajectories endowed with a suitable weight (such a setting is called
WKB-branch).
  The transformation properties of various quantities under a variation of the
WKB-branch provide the tool for defining the decomposition. The construction
leads to formal series whose actual convergence seems to require additional
conditions on the model (related to global geometric issues and possibly to
analyticity). It is speculated that this approach might relate to the refined
algebraic quantization program.
