## Neutrino Minimal Standard Model

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The Neutrino Minimal Standar Model (nuMSM or $\nu$MSM) is an extension of the Standard Model with three right-handed (or sterile) neutrinos. It aims to address within one consistent framework several problems beyond the Standard Model The Lagrangian of the $\nu$MSM is
Here $F_{\alpha I}$ are new Yukawa couplings, $L_\alpha$ are left-handed leptonic doublets, the index $\alpha =e,\mu ,\tau$ labels generations, $\phi$ is a Higgs doublet with $\tilde \phi _j = i(\tau _2)_{j}^k \phi ^*_k$. The right-handed neutrinos $N_I$ have zero electric, weak and strong charges. The Majorana masses$M_I$ are consistent with the gauge symmetries of the SM This is the see-saw Lagrangian, however the Majorana masses of the right-handed neutrinos are chosen to be below electroweak scale. The smallness of the neutrino masses is achieved via small Yukawa couplings.
See references [1, 2] for the original paper and [3] for the recent review
References:
• [1]^ T. Asaka and M. Shaposhnikov The nuMSM, dark matter and baryon asymmetry of the universe, Phys. Lett. B620:17-26 (2005) INSPIRE
• [2]^ T. Asaka, S. Blanchet and M. Shaposhnikov The nuMSM, dark matter and neutrino masses, Phys. Lett. B631:151-156 (2005) INSPIRE
• [3]^ A. Boyarsky, O. Ruchayskiy and M. Shaposhnikov, Ann. Rev. Nucl. Part. Sci. 59 (2009) 191 [arXiv:0901.0011]. INSPIRE