Effective theory of a doubly charged singlet scalar: complementarity of neutrino physics and the LHC

Abstract

We consider a rather minimal extension of the Standard Model involving just one extra particle, namely a single SU(2) L singlet scalar S ++ and its antiparticle S −− . We propose a model independent effective operator, which yields an effective coupling of S ±± to pairs of same sign weak gauge bosons, W ± W ± . We also allow tree-level couplings of S ±± to pairs of same sign right-handed charged leptons l ± R l ± R of the same or different flavour. We calculate explicitly the resulting two-loop diagrams in the effective theory responsible for neutrino mass and mixing. We propose sets of benchmark points for various S ±± masses and couplings which can yield successful neutrino masses and mixing, consistent with limits on charged lepton flavour violation (LFV) and neutrinoless double beta decay. We discuss the prospects for S ±± discovery at the LHC, for these benchmark points, including single and pair production and decay into same sign leptons plus jets and missing energy. The model represents a minimal example of the complementarity between neutrino physics (including LFV) and the LHC, involving just one new particle, the S ±± .

Systematic classification of two-loop realizations of the Weinberg operator

“…A possible connection between two-loop neutrino masses and dark matter has been explored in [53,54] in two models giving each a CLBZ-3 type diagram. Then there are also models, based on CLBZ, using vectors instead of scalars [55][56][57]. All these models are realizations of a 2-loop gauge-mediated diagram involving an internal effective coupling (see e.g.…”

“…Finally, ref. [57] considers a partial UV completion involving an effective lepton number-violating vertex for W bosons with a doubly charged singlet. Then there are models based on variants of PTBM such as [60], which uses leptoquarks and a colour octet fermion.…”

Running of radiative neutrino masses: the scotogenic model — revisited

“…In such models, the neutrino mass vanishes exactly at tree-level, but it is generated by loop-diagrams as a small correction to the tree-level Lagrangian. The easiest such models generate a neutrino mass at 1-loop [17,18], see [19] for a general classification, although 2-loop [20][21][22][23][24][25][26] 1 or 3-loop [28][29][30][31][32] mass generation is possible, too. 2 The most attractive point of radiative neutrino mass models is that they intrinsically connect the phenomenology of light neutrinos to other sectors.…”

Parity problem of the scotogenic neutrino model

“…Ref. [1] to see how such settings are constrained at both, low and high energies. Depending on the particle content, there exist models which generate an active neutrino mass at 1-loop [2], 2-loop [3,4], or 3-loop [5,6] level, but probably the simplest extension compatible with all data is Ma's scotogenic model [7].…”