Abstract
We study a model which generates Majorana neutrino masses at tree-level via low-energy effective operator with mass-dimension-9. Introduction of such a higher dimensional operator brings down the lepton number violating mass scale to TeV making such model potentially testable at present or near future colliders. This model possesses several new SU(2)L fermionic multiplets, in particular, three generations of triplets, quadruplets and quintuplets, and thus a rich phenomenology at the LHC. Noting that lepton flavour violation arises very naturally in such setup, we put constraints on the Yukawa couplings and heavy fermion masses using the current experimental bounds on lepton flavour violating processes. We also obtain 95% CL lower bounds on the masses of the triplets, quadruplets and quintuplets using a recent CMS search for multilepton final states with 137 inverse femtobarn integrated luminosity data at 13 TeV center of mass energy. The possibility that the heavy fermions could be long-lived leaving disappearing charge track signatures or displaced vertex at the future colliders like LHeC, FCC-he, MATHUSLA, etc. is also discussed.
Highlights
Magnetic moment of electron and muon, baryon asymmetry and dark matter
At a given dimension d, if all the lower dimensional contributions to neutrino masses are automatically absent without the need for any additional U(1) or Zn symmetry
We have studied a genuine model that generates neutrino masses at tree-level via lowenergy effective operator with mass-dimension-9
Summary
The block diagonalisation of the mass matrix (MN ) for the neutral leptons in eq (2.3) (see appendix A) gives rise to the following 3 × 3 Majorana mass matrix for light neutrinos at. Note that mν in eq (2.5) is suppressed by higher power of Λ (in particular, by Λ−5 at the leading order) which automatically brings down the new physics scale of Λ to TeV for reasonably large Yukawa couplings of O(10−1 − 10−2). This makes this model tastable at the collider experiments. We see that a number of parameters (6 parameters to be precise) get lost in decoupling of the heavy fields from high-energy to low-energy These otherwise lost information is encrypted in the arbitrary complex orthogonal matrix, R
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