Abstract
In this paper, we perform a detail analysis on leptogenesis and dark matter form low scale seesaw. In the framework of $\nu$2HDM, we further introduce one scalar singlet $\phi$ and one Dirac fermion singlet $\chi$, which are charged under a $Z_2$ symmetry. Assuming the coupling of $\chi$ is extremely small, it serves as a FIMP dark matter. The heavy right hand neutrinos $N$ provide a common origin for tiny neutrino mass (via seesaw mechanism), leptogenesis (via $N\to \ell_L \Phi_\nu^*,\bar{\ell}_L \Phi_\nu$) and dark matter (via $N\to \chi\phi$). With hierarchical right hand neutrino masses, the explicit calculation shows that success thermal leptogenesis is viable even for TeV scale $N_1$ with $0.4 \lesssim v_\nu\lesssim1$ GeV and lightest neutrino mass $m_1\lesssim 10^{-11}$ eV. In such scenario, light FIMP dark matter in the keV to MeV range is naturally expected. The common parameter space for neutrino mass, natural leptogenesis and FIMP DM is also obtained in this paper.
Highlights
Besides the success of the standard model (SM), there are still several open questions
We further introduce a dark sector with one scalar singlet φ and one Dirac fermion singlet χ, which are charged under a Z2 symmetry [37,38]
One scalar singlet φ and one Dirac fermion singlet χ are further introduced, which are charged under a Z2 symmetry
Summary
Besides the success of the standard model (SM), there are still several open questions. Leptogenesis with hierarchal right-hand neutrinos, an upper limit on the charge-parity (CP) asymmetry exists; a lower limit on the mass of lightest right-hand neutrino M1 should be satisfied [6], M1 Both tiny neutrino mass and leptogenesis favor the high scale N in the type-I seesaw mechanism. One viable pathway to overcome this is lowering the leptogenesis scale by imposing resonant leptogenesis [9], an Akhmedov-Rubakov-Smirnov mechanism via neutrino oscillation [10,11], or Higgs decay [12,13] The success of these scenarios depends on the degenerate mass of right-hand neutrinos [14,15], which seems is another sense of unnaturalness.
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