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 mW​ .
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 O(100) GeV new particles are allowed in the scalar extension
scenarios.Comment: 24 pages, 4 figure