Testing the Zee-Babu model via neutrino data, lepton flavour violation and direct searches at the LHC

Juan Herrero-Garcia,Miguel Nebot,Nuria Rius,Arcadi Santamaria

doi:10.1016/j.nuclphysbps.2015.09.271

Abstract

In this talk we discuss how the Zee-Babu model can be tested combining information from neutrino data, low-energy experiments and direct searches at the LHC. We update previous analysis in the light of the recent measurement of the neutrino mixing angle θ13 [1], the new MEG limits on μ→eγ [2], the lower bounds on doubly-charged scalars coming from LHC data [3, 4], and, of course, the discovery of a 125 GeV Higgs boson by ATLAS and CMS [5, 6]. In particular, we find that the new singly- and doubly-charged scalars are accessible at the second run of the LHC, yielding different signatures depending on the neutrino hierarchy and on the values of the phases. We also discuss in detail the stability of the potential.

Highlights

Where c encodes some lepton number violating (LNV) couplings and/or ratios of masses, Λ is the scale of LNV which can be at the TeV and can be accessible at colliders, and i are the number of loops, where typically more than three loops yield too light neutrino masses or have problems with low-energy constraints
We have studied the ZB model in the light of the second run of the LHC, taking into account the new available data from low-energy and neutrino experiments, and from direct searches
The scalar masses are accessible to LHC-14 in both hierarchies, but input information from neutrino experiments is crucial to really pin-down the model

Summary

Introduction

Radiative models are a very plausible way in which neutrinos may acquire their tiny masses: ν’s are light because they are massless at tree level, with their masses being generated by loop corrections that generically have the following form: mν. For a given set of parameters defined at the electroweak scale, and satisfying the stability conditions discussed above, one can calculate the running couplings numerically by using one-loop RGEs. The new scalar couplings λhH, λkH always contribute positively to the running of the Higgs quartic coupling λH, compensating for the large and negative contribution of the top quark Yukawa coupling. To see how neutrino masses can be generated in this model, it is important to remark that lepton number violation requires the simultaneous presence of the four couplings Y, f , g and μ, because if any of them vanishes one can always assign quantum numbers in such a way that there is a global U(1) symmetry. At least one of the neutrinos is exactly massless at this order

Constraints on the parameters of the model

Numerical scan

Conclusions