Electroweak precision tests for triplet scalars

TL;DR

This paper investigates how triplet scalars in extensions of the Standard Model can explain the W mass anomaly by affecting electroweak precision observables, especially the oblique parameters S, T, U, through global fits.

Contribution

It provides a detailed analysis of the impact of hyper-charge Y=1 and Y=0 triplet scalars on electroweak precision tests and the W mass anomaly, including parameter space constraints.

Findings

Triplet scalars can significantly modify oblique parameters at tree and loop levels.

The models can accommodate the W mass excess observed by CDF.

The global fit indicates the necessity of new physics beyond the Standard Model.

Abstract

Electroweak precision observables are fundamentally important for testing the standard model (SM) or its extensions. The influences to observables from new physics within the electroweak sector can be expressed in terms of oblique parameters S, T, U. The recently reported W mass excess anomaly by CDF modifies these parameters in a significant way. By performing the global fit with the CDF new W mass measurement data, we obtain $S=0.03 \pm 0.03$, $T=0.06 \pm 0.02$ and $U=0.16 \pm 0.03$ (or $S=0.14 \pm 0.03$, $T=0.24 \pm 0.02$ with $U=0$) which is significantly away from zero as SM would predict. The CDF excess strongly indicates the need of new physics beyond SM. We carry out a global fit to study the influence of two different cases of simple extensions by a hyper-charge $Y=1$ triplet scalar $\Delta$ (corresponding to the type-II seesaw model) and a $Y=0$ real triplet scalar $\Sigma$ on electroweak precision tests to determine parameter space in these models to solve the W mass anomaly and discuss the implications. We find that these triplets can affect the oblique parameters significantly at the tree and loop levels.