Novel constraint on the parameter space of the Georgi-Machacek model with current LHC data

The same-sign diboson process pp→W^±W^±jj has been measured at the LHC using leptonic decay channels of W bosons, with production cross sections of two fiducial regions reported to be consistent with the Standard Model expectations within 1σ. These results constrain new physics models with a modified W⁺W⁺W^-W^- vertex. We consider in particular the Georgi-Machacek model in which the quartic W boson vertex is effectively modified due to mediations of new Higgs bosons in the model. The relevant gauge-gauge-scalar couplings are all proportional to the vacuum expectation value of the isospin triplets, which can be of O(10) GeV because of custodial vacuum alignment. Using the current 8-TeV data at the LHC, we exclude parameter space on the plane of the triplet vacuum expectation value and the new Higgs boson mass. The expected discovery reach at the 14-TeV LHC is also studied.