Explanation of the W mass shift at CDF II in the extended Georgi-Machacek model

The CDF II experiment has recently determined the mass of the W boson to be mW(CDF II) = 80.4335 +/- 0.0094 GeV, which deviates from the standard model prediction at 7 sigma level. Although this new result is in tension with other experiments such as those at LHC and LEP, it is worth discussing possible implications on new physics by this anomaly. We show that this large discrepancy can be explained by nonaligned vacuum expectation values of isospin triplet scalar fields in the Georgi-Machacek model extended with custodial symmetry-breaking terms in the potential. The latter is required to avoid an undesirable Nambu-Goldstone boson as well as to be the consistent treatment of radiative corrections. With mW(CDF II) as one of the renormalization inputs at the one-loop level, we derive the required difference in the triplet vacuum expectation values, followed by a discussion of phenomenological consequences in the scenario.

Automated summary

The recent measurement of the mass of the W boson by the CDF II experiment deviates from the predicted value in the standard model, suggesting the existence of new physics. A possible explanation for this discrepancy is the nonaligned vacuum expectation values of isospin triplet scalar fields in the Georgi-Machacek model with custodial symmetry-breaking terms in the potential.