Searching for radiative neutrino mass generation at the LHC

Abstract

In this talk, I describe the general characteristics of radiative neutrino mass models that can be probed at the LHC. I then cover the specific constraints on a new, explicit model of this type.Keywords: Neutrino; radiative mass generation; effective operators; flavor-violation constraints; LHC constraints See-saw versus radiative neutrino mass generationMany models of radiative neutrino mass are possible, some of which have been analysed in depth, while others have been examined only briefly, with quite a number yet to be explicitly written down let alone analysed. A useful organising principle for Majorana neutrino mass models is to use standard model (SM) effective operators that violate lepton number conservation by two units (∆L = 2 operators) as a base from which to construct new theories. 1-7Restricting ourselves to operators containing SM fermions and a single Higgs doublet, they occur at odd mass dimensions, with the lowest order one occurring at d = 5. That operator is the famous Weinberg operator, which has the schematic structure LLHH, where L is a lepton doublet and H the Higgs doublet. After electroweak symmetry breaking, this operator (actually a set of operators because of the family structure) directly induces a Majorana neutrino mass for left-handed (LH) neutrinos given by the see-saw formula,where M is the scale of the new physics that gives rise to the operator in the low-energy limit. Underlying renormalisable theories yielding LLHH are constructed by "opening up" the operator. The type-1,-2 and -3 see-saw models are the minimal, tree-level ways to open up LLHH. [8][9][10][11][12][13][14][15][16][17][18][19] By starting with the effective operator, one may systematically construct all of the minimal underlying models.Other ∆L = 2 effective operators have mass dimension seven or higher and feature other lepton and quark fields in their expression, except for those in the