Minimal model for the W-boson mass, (g-2)μ, h→μ+ μ-, and quark-mixing-matrix unitarity

The SU(2) (L) triplet scalar with hypercharge Y = 0 predicts a positive definite shift in the W mass, with respect to the Standard Model prediction, if it acquires a vacuum expectation value. As this new field cannot couple directly to Standard Model fermions (on its own), it has no significant impact on other low-energy precision observables and is weakly constrained by collider searches. In fact, the multilepton anomalies at the LHC even point toward new scalars that decay dominantly to W bosons, as the neutral component of the triplet naturally does. In this article, we show that with a minimal extension of the scalar triplet model by a heavy vectorlike lepton, being either (I) an SU(2) (L) doublet with Y = -1/2 or (II) an SU(2) L triplet with Y = -1, couplings of the triplet to Standard Model leptons are possible. This minimal extension can then provide, in addition to the desired positive shift in the W mass, a chirally enhanced contribution to (g - 2)(mu). In addition, versions (I) and (II) can improve on Z ->mu(+)mu(-) and alleviate the tension in first-row CabibboKobayashi-Maskawa unitarity (known as the Cabibbo angle anomaly), respectively. Finally, both options, in general, predict sizable changes of h ->mu(+) mu(-), i.e., much larger than most other (g - 2) (mu) explanations where only O%THORN effects are expected, making this channel a smoking gun signature of our model.