Understand
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 $c \sim \mathcal{O}(1)$.