Testing the custodial symmetry in the Higgs sector of the Georgi-Machacek model

Abstract

We study how the custodial symmetry in the Higgs sector of the Georgi-Machacek (GM) model can be tested at the LHC. As the minimal extension of the Higgs triplet model, in which tiny neutrino masses are generated via the Type-II Seesaw Mechanism, the GM model keeps the electroweak [rho] parameter at unity at tree level. In the GM model, there are 5-plet (H ^sub 5^), 3-plet (H ^sub 3^) and singlet (H ^sub 1^) Higgs bosons under the classification of the custodial SU(2)^sub V^ symmetry, in addition to the standard model-like Higgs boson (h). These new Higgs bosons have the following characteristic features at the tree level: (1) the masses of the Higgs bosons belonging to the same SU(2)^sub V^ multiplet are degenerate; and (2) H ^sub 5^ and H ^sub 1^ couple to the electroweak gauge bosons but not SM quarks, whereas H ^sub 3^ couples to the quarks but not the gauge bosons. We find that the H ^sub 5^ production from the weak vector boson fusion process and the Drell-Yan process associated with H ^sub 3^ are useful in testing the custodial symmetry of the Higgs sector at the LHC. In addition, these processes can also be used to discriminate from other models that contain singly-charged Higgs bosons and extra neutral Higgs bosons. We also investigate a possible enhancement in the h [arrow right] γγ as well as h [arrow right] Zγ decays.