  We consider a Lagrangian of interacting scalar fields. We divide the
Lagrangian into two parts. The first part is to describe either the dark matter
(DM) or the inflaton (IN) depending on the choice of the self-interaction. The
second part constitutes an environment of an infinite number of scalar fields
interacting linearly with the first part. We approximate the environment by a
white noise obtaining a Langevin equation. We show that the resulting
Fokker-Planck equation has solutions determining a relation between the
diffusion constant, the cosmological constant and the temperature. As a
consequence of the Langevin approximation the energy-momentum tensor of the
dark matter and the inflaton is not conserved. The compensating energy-momentum
tensor is interpreted as the dark energy (DE). We insert the total
energy-momentum in Einstein equations. We show that under special initial
conditions Einstein equations have a solution with a constant ratio of DM/DE
and IN/DE densities.
