Right-handed neutrinos and the CDF II anomaly

Understand

We point out that right-handed neutrinos can resolve the tension between the latest CDF II measurement of the $W$-boson mass, $M_W$, and the standard model.

• Integrating out the new states yields a single $d=6$ operator, which induces a deviation from unitarity in the PMNS matrix.
• This alters the extraction of the Fermi constant from muon decay and increases the prediction for $M_W$, in line with the CDF II result.
• Non-unitarity of the PMNS matrix would also affect beta, meson, and tau decays.