  We investigate the interaction between dark energy and dark matter in the
framework of irreversible thermodynamics of open systems with matter
creation/annihilation. We consider dark energy and dark matter as an
interacting two component (scalar field and "ordinary" dark matter)
cosmological fluid in a homogeneous spatially flat and isotropic
Friedmann-Robertson-Walker (FRW) Universe. The thermodynamics of open systems
as applied together with the gravitational field equations to the two component
cosmological fluid leads to a generalization of the elementary dark energy-dark
mater interaction theory, in which the decay (creation) pressures are
explicitly considered as parts of the cosmological fluid stress-energy tensor.
Specific models describing coherently oscillating scalar waves, leading to a
high particle production at the beginning of the oscillatory period, and models
with a constant potential energy scalar field are considered. Furthermore,
exact and numerical solutions of the gravitational field equations with dark
energy-dark matter interaction are also obtained.
