Enhancement of the $\textbf{W}$ boson mass in the Georgi-Machacek model

Abstract: The recent CDF-II measurement of the mass of the $W$ boson shows a significant tension with the Standard Model (SM) expectation, even when averaged with earlier measurements. The tension can be explained in the framework of any beyond-SM dynamics that contributes substantially to the oblique $S$ and $T$ parameters. As a typical example of such beyond-SM physics, we try to explain the tension in the framework of the Georgi-Machacek model that keeps $\rho=1$ at the tree-level, and explore the parameter space that can accommodate the $W$ mass shift. We find that a sizeable split between the custodial triplet and 5-plet of scalars can help alleviate the tension to a large extent, and raise the $W$-mass by about 30 MeV over its SM value.