The multi-feature universe: Large parameter space cosmology and the swampland

Abstract

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 ΛCDM cosmology, in light of current observations. We obtain the largest 2σ (3σ) bound so far, c≲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)×O(16) heterotic string and some Type II string compactifications. For inflationary models with concave potential, we find the 2σ (3σ) bound c≲0.13 (0.14), which is still in strong tension with the string-based expectation c∼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 2σ (3σ) bound c≲0.53 (0.58), which is now in a modest tension with the swampland conjecture.