Dark energy states from quantization of boson fields in a universe with unstable modes

It is shown that the classical, generally covariant massless Klein-Gordon field develops unstable modes when it is non-conformally coupled to the geometry of an expanding and accelerating universe. Second quantization then leads to a canonical Hamiltonian that is naturally partitioned into a light component and a dark component; the spatial spectrum of the latter consisting of a broadening band of low wave numbers. The dark component has fundamental subsystems that are repulsive units with time-varying force constant. The spectrum of the repulsive units is continuous and unbounded below. There are no long-lasting dark particle states with conserved number operators, so that detection by absorption of energy quanta is not feasible unless the energy is transferred to a coupled stable field.