  We introduce a toy model of scalar particles with a trilinear scalar coupling
in cosmology. The trilinear coupling $\phi^2\chi$ causes production of
non-relativistic $\phi$ particles through the process
$\chi\chi\,\rightarrow\,\phi\phi$ where, initially, only relativistic $\chi$
particles are present. We consider the initial times of
$\chi\chi\,\rightarrow\,\phi\phi$ and observe that the curved space effects
promote formation of Bose-Einstein condensate of $\phi$ particles.
