Basis-independent methods for the two-Higgs-doublet model III: The CP-conserving limit, custodial symmetry, and the oblique parameters S, T, U

Understand

In the Standard Model, custodial symmetry is violated by the hypercharge U(1) gauge interactions and the Yukawa couplings, while being preserved by the Higgs scalar potential.

• In the two-Higgs doublet model (2HDM), the generic scalar potential introduces new sources of custodial symmetry breaking.
• We obtain a basis-independent expression for the constraints that impose custodial symmetry on the 2HDM scalar potential.
• These constraints impose CP-conservation on the scalar potential and vacuum, and in addition add one extra constraint on the scalar potential parameters.