In this talk, I will review a series of papers (in particular 2205.12293 and 2507.03090) discussing the Dark Dimension Scenario conjecturing that our universe is embedded in a five-dimensional spacetime whose extra dimension is mesoscopic.
A natural dark matter candidate within this model is given by the Kaluza-Klein excitation modes of the graviton along the extra dimension whereas the 4D cosmological constant can be parametrized by the size of the extra dimension.
Being discussed as a purely theoretical construction, motivated from non-supersymmetric string theory, this scenario gained new attention as its predictions seem to be in excellent agreement with experimental data from the DESI DR2 and SN measurements.