Abstract
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)μ. In addition, versions (I) and (II) can improve on Z→μ+μ− and alleviate the tension in first-row Cabibbo-Kobayashi-Maskawa unitarity (known as the Cabibbo angle anomaly), respectively. Finally, both options, in general, predict sizable changes of h→μ+μ−, i.e., much larger than most other (g−2)μ explanations where only O(%) effects are expected, making this channel a smoking gun signature of our model.
Crivellin, Andreas