Evolving Dark Sector and the Dark Dimension Scenario

Understand

String theory naturally leads to the expectation that dark energy is not stable, and may be evolving as captured by the Swampland de Sitter conjectures.

• Moreover, motivated by the distance conjecture, a unification of dark sector has been proposed, where the smallness of dark energy leads to one extra dimension of micron size with dark matter being the Kaluza--Klein graviton excitations in this extra dimension.
• We consider the natural possibility that the radius of the dark dimension varies as the energy decreases, leading to the variation of the dark matter mass.
• This correlates the variation of the dark energy with the variation of the dark matter mass as they depend on the variations of a scalar field $\phi$ controlling the radius of the extra dimension.