  Regarding long life particles produced during preheating after inflation as
dark matter, we find that its back reaction on the field $\phi$ could lock
$\phi$ in a false vacuum up to today. This false vacuum can drive the
accelerated expansion of universe at late time and play the role of dark
energy. When the number density of dark matter particles is dilute to some
value, the field $\phi$ becomes tachyonic and rolls to its true minima rapidly,
and the acceleration of universe ceases. We discuss the constraints on the
parameters of model from the observations of dark energy and dark matter halos
on subgalactic scale.
