  We consider a variant of seesaw mechanism by introducing extra singlet
neutrinos and singlet scalar boson, and show how low scale leptogenesis is
successfully realized in this scenario. We examine if the newly introduced
neutral particles, either singlet Majorana neutrino or singlet scalar boson,
can be a candidate for dark matter. We also discuss the implications of the
dark matter detection through the scattering off the nucleus of the detecting
material on our scenarios for dark matter. In addition, we study the
implications for the search of invisible Higgs decay at LHC, which may serve as
a probe of our scenario for dark matter.
