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 $S^{\pm \pm }$ to pairs of same sign weak gauge bosons, $W^{\pm }{W}^{\pm }$. We also allow tree-level couplings of $S^{\pm \pm }$ to pairs of same sign right-handed charged leptons $l_R^{\pm }{l}_R^{\prime \pm }$ 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 $S^{\pm \pm }$ 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 $S^{\pm \pm }$ 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 $S^{\pm \pm }$.

Comments: 57 pages, 14 figures, 10 tables, version accepted for publication in JHEP