Constraints on Multicomponent Dark Energy from Cosmological Observations
  Dark energy (DE) plays an important role in the expansion history of our
universe. But we only got limited knowledge about its nature and properties
after decades of study.In most numerical researches, DE is usually considered
as a dynamical whole. Actually, multicomponent DE models can also explain the
accelerating expansion of our universe, which is accepted theoretically but
lack of numerical researches. We try to study the multicomponent DE models from
observation by constructing $w_n$CDM models. The total energy density of DE is
separated into $n$ ($n=2,3,5$) parts equally and every part has a constant EOS
$w_i$ ($i=1,2...n$). We modify the Friedmann equation and the parameterized
post-Friedmann description of DE, then put constraints on $w_i$s from Planck
2018 TT,TE,EE$+$lowE$+$lensing, BAO data and PANTHEON samples. The
multicomponent DE models are favoured if any $w_n$CDM model is preferred by
observational data and there is no overlap between the highest and lowest
values of $w_i$s. We find the data combination supports the $w_n$CDM model when
$n$ is small and the $w_2$CDM model is slightly preferred by $\Delta
\chi^2_{\text{min}} = \Delta \text{AIC} =\Delta \text{BIC} = -2.48$ over the
CPL model, but the largest value of $w_i$ overlaps the smallest one. With
larger $n$, the maximum and minimum of $w_i$s do not overlap with each other,
but $\chi^2_{\text{min}}$ and AIC also increase. In brief, we find no obvious
evidence that DE is composed of different components.
