A vector-like fourth generation with a discrete symmetry from Split-UED

Understand

Split-UED allows for the possibility that the lowest lying KK excitations of the Standard Model fermions can be much lighter than the corresponding gauge or Higgs KK states.

• This can happen provided the fermion bulk masses are chosen to be large, in units of the inverse compactification radius, 1/R, and negative.
• In this setup, all of the other KK states would be effectively decoupled from low energy physics.
• Such a scenario would then lead to an apparent vector-like fourth generation with an associated discrete symmetry that allows us to accommodate a dark matter candidate.