Custodial Symmetry Violation in Scalar Extensions of the Standard Model

TL;DR

This paper investigates how scalar extensions of the Standard Model can explain the recent W boson mass measurement discrepancy, focusing on custodial symmetry violation and its effects on electroweak precision data.

Contribution

It analyzes scalar sector extensions with and without custodial symmetry, showing how they fit electroweak data and accommodate new particles around 100 GeV.

Findings

Large mass splittings or VEVs can explain the W mass anomaly.

Scalar extensions with custodial symmetry are compatible with data.

New particles around 100 GeV are allowed in these models.

Abstract

The new measurement of the W boson mass from the CDF collaboration shows a significant tension with the Standard Model prediction, which evidences violation of custodial symmetry in the scalar sector. We study the scalar extensions of the Standard Model, which can be categorized into two classes, scalar sector with custodial symmetry (Georgi-Machacek model and its generalizations) and scalar sector without custodial symmetry, and explore how these extensions fit to the electroweak precision data and the CDF new $m_W$ . The favored oblique parameters are coming from either the large mass splitting in the multiplet via the loop contribution or the large vacuum expectation value which breaks custodial symmetry at the tree level. In particular, we find that $\mathcal{O}(100)$ GeV new particles are allowed in the scalar extension scenarios.