Neutrino masses and the CERN LHC: Testing the type II seesaw mechanism

By P. Pérez, T. Han, Gui-Yu Huang, Tong Li, Kai Wang. 2008

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We demonstrate how to systematically test a well-motivated mechanism for neutrino mass generation (type II seesaw) at the LHC, in which a Higgs triplet is introduced. In the optimistic scenarios with a small Higgs triplet vacuum expectation value ${v}_{\ensuremath{\Delta}}l{10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{GeV}$, one can look for clean signals of lepton-number violation in the decays of doubly charged (${H}^{\ifmmode\pm\else\textpm\fi{}\ifmmode\pm\else\textpm\fi{}}$) and singly charged (${H}^{\ifmmode\pm\else\textpm\fi{}}$) Higgs bosons to distinguish the normal hierarchy (NH), the inverted hierarchy (IH), and the quasidegenerate (QD) spectrum for the light neutrino masses. The observation of either ${H}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}\overline{\ensuremath{\nu}}$ or ${H}^{+}\ensuremath{\rightarrow}{e}^{+}\overline{\ensuremath{\nu}}$ will be particularly robust for the spectrum test since they are independent of the unknown Majorana phases. The ${H}^{++}$ decays moderately depend on a Majorana phase ${\ensuremath{\Phi}}_{2}$ in the NH, but sensitively depend on ${\ensuremath{\Phi}}_{1}$ in the IH. In a less favorable scenario ${v}_{\ensuremath{\Delta}}g2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{GeV}$, when the leptonic channels are suppressed, one needs to observe the decays ${H}^{+}\ensuremath{\rightarrow}{W}^{+}{H}_{1}$ and ${H}^{+}\ensuremath{\rightarrow}t\overline{b}$ to confirm the triplet-doublet mixing which in turn implies the existence of the same gauge-invariant interaction between the lepton doublet and the Higgs triplet responsible for the neutrino mass generation. In the most optimistic situation, ${v}_{\ensuremath{\Delta}}\ensuremath{\sim}{10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{GeV}$, both channels of the lepton pairs and gauge boson pairs may be available simultaneously. The determination of their relative branching fractions would give a measurement for the value of ${v}_{\ensuremath{\Delta}}$.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a8b6db041ea6eb6ee9191a55fe49b7fd2aef353f