Singlet extensions and W boson mass in the light of the CDF II result

TL;DR

This paper investigates whether singlet extensions of the Standard Model can explain the recent CDF II W boson mass measurement discrepancy, finding that such models cannot fully account for the observed shift.

Contribution

The study analyzes the impact of singlet extensions on the W boson mass and evaluates the constraints, showing they cannot resolve the CDF II anomaly.

Findings

W mass shift in minimal singlet models is at most a few MeV.

Allowing invisible decays of the singlet does not increase the W mass beyond 5 MeV.

Singlet extensions have implications for dark matter and cosmology, but do not fully explain the W mass discrepancy.

Abstract

Recently, the CDF collaboration has reported the precise measurement of the W boson mass, $M_W = 80433.5\pm 9.4 \,$MeV, based on $8.8$ fb$^{-1}$ of $\sqrt{s}=1.96$ TeV $p\bar{p}$ collision data from the CDF II detector at the Fermilab Tevatron. This is about $7\sigma$ away from the Standard Model prediction, $M_{W}^{\rm SM}=80357 \pm 6 \,$MeV. Such a large discrepancy may be partially due to exotic particles that radiatively alter the relation between the W and Z boson masses. In this Letter, we study singlet extensions of the Standard Model focusing on the shift of the W boson mass. In the minimal extension with a real singlet field, using the bounds from the electroweak oblique parameters, B meson decays, LEP, and LHC, we find that the W boson mass shift is at most a few MeV, and therefore it does not alleviate the tension between the CDF II result and the SM prediction. We then examine how much various bounds are relaxed when the singlet is allowed to decay invisibly and find that the increase of the W boson mass does not exceed $5$ MeV due to the bound from the Higgs signal strength. We also discuss phenomenological and cosmological implications of the singlet extensions such as the muon $g-2$ anomaly, axion/hidden photon dark matter, and self-interacting dark radiation as a possible alleviation of the Hubble tension.