  In this paper we present a realization of dark dimension. We consider the 5D
standard model coupling to gravity with one dimension compactified on an
orbifold, which is seen as dark dimension of size R. We stabilize the radion by
casimir effect wrapping around compact dimension and recover the neutrino mass
and 4D cosmological constant with the observed value. Orbifold can lead to a
natural resolution of chirality problem in 5D at low energy, which we briefly
discussed in the paper. Although we found that the radion mass is too light to
survive under solar system tests of GR, several screening mechanisms might give
us a solution, for example, Chameleon mechanism.
