Multi-feature universe: large parameter space cosmology and the
  swampland
  Under the belief that the universe should be multi-feature and informative,
we employ a model-by-model comparison method to explore the possibly largest
upper bound on the swampland constant $c$. Considering the interacting
quintessence dark energy as the comparison model, we constrain the large
parameter space interacting dark energy model, a 12-parameter extension to the
$\Lambda$CDM cosmology, in light of current observations. We obtain the largest
$2\sigma$ ($3\sigma$) bound so far, $c\lesssim1.62$ $(1.94)$, which would allow
the existences of a number of string theory models of dark energy such as
11-dimensional supergravity with double-exponential potential, $O(16)\times
O(16)$ heterotic string and some Type II string compactifications. For
inflationary models with concave potential, we find the $2\sigma$ ($3\sigma$)
bound $c\lesssim0.13$ $(0.14)$, which is still in strong tension with the
string-based expectation $c \sim \mathcal{O}(1)$. However, combining Planck
primordial non-Gaussianity with inflation constraints, it is interesting that
the Dirac-Born-Infeld inflation with concave potential gives the $2\sigma$
($3\sigma$) bound $c\lesssim0.53$ $(0.58)$, which is now in a modest tension
with the swampland conjecture. Using the Bayesian evidence as the model
selection tool, it is very surprising that our 18-parameter multi-feature
cosmology is extremely strongly favored over the $\Lambda$CDM model.
