Co-genesis of Matter and Dark Matter with Vector-like Fourth Generation
  Leptons
  We propose a simple extension of the standard model by adding a fourth
generation vector-like lepton doublet and show that if the fourth neutrino is a
massive pseudo-Dirac fermion with mass in the few hundred GeV range and mass
splitting of about 100 keV, its lighter component can be a viable inelastic
dark matter candidate. Its relic abundance is produced by the CP violating
out-of-equilibrium decay of the type-II seesaw scalar triplet, which also gives
rise to the required baryon asymmetry of the Universe via type-II leptogenesis,
thus providing a simultaneous explanation of dark matter and baryon abundance
observed today. Moreover, the induced vacuum expectation value of the same
scalar triplet is responsible for the sub-eV Majorana masses to the three
active neutrinos. A stable fourth generation of neutrinos is elusive at
collider, however might be detected by current dark matter direct search
experiments.
