  Cosmological runaway solutions may exhibit an exact dilatation symmetry in
the asymptotic limit of infinite time. In this limit, the massless dilaton or
cosmon could be accompanied by another massless scalar field - the geon. At
finite time, small time-dependent masses for both the cosmon and geon are still
present due to imperfect dilatation symmetry. For a sufficiently large mass the
geon will start oscillating and play the role of dark matter, while the cosmon
is responsible for dark energy. The common origin of the mass of both fields
leads to an effective interaction between dark matter and dark energy.
Realistic cosmologies are possible for a simple form of the effective
cosmon-geon-potential. We find an inverse geon mass of a size where it could
reduce subgalactic structure formation.
