  We extend previous studies of big bang nucleosynthesis, with the assumption
that ordinary matter and dark matter sectors are entangled through the number
of degrees of freedom entering the Friedmann equations. This conjecture allows
us to find a relation between the temperatures of the weakly interacting matter
and dark-matter sectors. The constraints imposed by observations are studied by
comparison with calculations of big bang nucleosynthesis for the abundance of
light elements. It is found that these constraints are compatible with cold
dark matter and a wide range number of dark sectors.
