Dark Energy, the Swampland and the Equivalence Principle
  It has recently been argued that string theory does not admit de Sitter
vacua. This would imply that the current accelerated expansion of the universe
is not driven by a cosmological constant (or vacuum energy) but by other means
such as a quintessential scalar field. Such a scalar field is in general
expected to couple to at least some matter species, such as dark matter.
Cosmological observations already constrain such dark matter couplings
strongly. We argue that there are a number of interesting scenarios to be
explored, such as coupling functions which possess a minimum at finite field
values. In these theories, the effective gravitational coupling between dark
matter particles grows with time and are consistent with observations of the
anisotropies in the cosmic microwave background radiation and large scale
structures. We argue that such couplings might also help to alleviate the
tension between the swampland conjectures and the properties of the
quintessential potential. Observational signatures of violations of the
equivalence principle in the dark sector are expected in the non-linear regime
on intermediate or small scales.
