Neutrino mass from neutrinophilic Higgs and leptogenesis
  In a class of two Higgs doublet model, where one Higgs doublet generates
masses of quarks and charged leptons whereas the other Higgs doublet with a
tiny vacuum expectation value (VEV) generates neutrino Dirac masses, smallness
of neutrino masses might be understand as the consequence of the small second
Higgs VEV. In this framework, thermal leptogenesis scenarios work well at low
energy scale and have several advantages as follows. Under the assumption of
hierarchical right-handed neutrino masses, the lightest right-handed neutrino
can be as light as ${\cal O}(10^2)$ TeV.The required degeneracy for successful
resonant leptogenesis also can be significantly reduced as small as ${\cal
O}(10^4)$. Availability of low scale thermal leptogenesis provides a novel
solution to gravitino problem in supergravity models.
