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 \lesssim 1.62 ( 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 \lesssim 0.13 ( 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 \lesssim 0.53 ( 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 .