Right-handed neutrinos at CERN LHC and the mechanism of neutrino mass generation

Abstract

We consider the possibility to detect right-handed neutrinos, which are mostly singlets of the Standard Model gauge group, at future accelerators. Substantial mixing of these neutrinos with the active neutrinos requires a cancellation of different contributions to the light neutrino mass matrix at the level of 10 −8 . We discuss possible symmetries behind this cancellation and argue that for three right-handed neutrinos they always lead to conservation of total lepton number. Light neutrino masses can be generated by small perturbations violating these symmetries. In the most general case, LHC physics and the mechanism of neutrino mass generation are essentially decoupled; with additional assumptions, correlations can appear between collider observables and features of the neutrino mass matrix.

Muon conversion to electron in nuclei in type-I seesaw models

“…[44,45] (see also Refs. [38][39][40]43]) is very predictive. The mixing-dependence of Br(h → νN ) -the term between parenthesis in Eq.…”

“…Nevertheless it turns out that the models which can naturally give measurable rates are models which involve two or more quasi-degenerate right-handed neutrinos and for these models one can make remarkably clear predictions. The quasi-degenerate case is particularly natural, as it takes place for instance in scenarios in which lepton number (L) is approximately conserved [33][34][35][36][37][38][39][40][41][42][43][44]: the degeneracy is protected by the symmetry. This assumption allows a natural decoupling between large Yukawa couplings (inducing L-preserving large rates) and small Yukawa couplings (guaranteeing small neutrino masses) and results in viable scenarios, even for low seesaw scales.…”

Fitting neutrino physics with a U(1) R lepton number

“…This is an example of inverse seesaw mechanism [41][42][43][44][45][46][47][48], where the role of the right handed Dirac neutrinos is played by the Dirac gauginos. Therefore, the tree level mass matrix in the PMRB scenario is:…”

Anomaly-Free Constraints in Neutrino Seesaw Models

“…The latter interactions are expected to be very suppressed and lead to unobservable production rates of the heavy fields, if the extra Uð1Þ gauge symmetry is broken at TeV energies. In this scenario, the seesaw mechanism could still be natural if some flavor symmetries that correctly reproduce the light neutrino masses, while keeping sizable Yukawa couplings, are invoked [12]. Clearly, there is much more phenomenology with the seesaw than the one considered here.…”