The $\rho$ parameter and the CDF W-mass anomaly: observations on the role of scalar triplets

Abstract

The $\rho$-parameter, together with the W-and Z-masses, acts as Occam's razor on extensions of the electroweak symmetry breaking sectors. We apply this to non-doublet Higgs scenarios, by examining the CDF- $II$ claim on the W-boson mass. Suspending any judgement on the CDF claim, we show that in general, if one works at the tree level, theoretical models which predict $\rho =1$ at the tree-level are inconsistent with the CDF claims at 4-6 standard deviations if one confines oneself to the existing Z-boson mass, and the earlier $M_W$ value from either the global fit or the ATLAS data. We take some well-motivated scenarios containing one or more scalar SU(2) triplets in addition to the usual doublet, and show that, both a scenario including a complex scalar triplet and one with a complex as well as a real triplet (the Georgi-Machacek model) can be made consistent with the new data, where a small splitting between the complex and the real triplet vacuum expectation values is required in the second scenario. We will explore the consequences of this splitting, either at tree level or via incalculable new physics contribution to $M_W$, and indicate, as illustrations its implications in $H^{\pm}W^{\mp}Z$ type interaction vertices.