  In the standard model of cosmology, the universe is described by a
Robertson-Walker spacetime, while its matter/energy content is modeled by a
perfect fluid with three components corresponding to matter/dust, radiation and
a cosmological constant. On the other hand, in particle physics matter and
radiation are described in terms of quantum field theory on Minkowski
spacetime. We unify these seemingly different theoretical frameworks by
analysing the standard model of cosmology from first principles within quantum
field theory on curved spacetime: assuming that the universe is homogeneous and
isotropic on large scales, we specify a class of quantum states whose
expectation value of the energy density is qualitatively and quantitatively of
the standard perfect fluid form up to potential corrections. Qualitatively,
these corrections depend on new parameters not present in the standard Lambda
CDM-model and can account for e.g. the phenomenon of Dark Radiation
(N_eff>3.046), having a characteristic signature which clearly deviates from
other potential Dark Radiation sources such as e.g. sterile neutrinos.
Quantitatively, we find that our more fundamental model can be perfectly
matched to observational data, such that we arrive at a natural and fundamental
extension of the Lambda CDM-model.
