Minimal model for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>W</mml:mi></mml:math>-boson mass, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">(</mml:mo><mml:mi>g</mml:mi><mml:mo>−</mml:mo><mml:mn>2</mml:mn><mml:msub><mml:mo stretchy="false">)</mml:mo><mml:mi>μ</mml:mi></mml:msub></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>h</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:msup><mml:mi>μ</mml:mi><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mi>μ</mml:mi><mml:mo>−</mml:mo></mml:msup></mml:math>, and quark-mixing-matrix unitarity

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 $Y=\ensuremath{-}1/2$ or (II) an $SU(2{)}_{L}$ triplet with $Y=\ensuremath{-}1$, 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 $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$. In addition, versions (I) and (II) can improve on $Z\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ 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 $h\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, i.e., much larger than most other $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ explanations where only $O(%)$ effects are expected, making this channel a smoking gun signature of our model.

Topics & Concepts