Testing the electroweak phase transition in scalar extension models at lepton colliders

Understand

We study the electroweak phase transition in three scalar extension models beyond the Standard Model.

• Assuming new scalars are decoupled at some heavy scale, we use the covariant derivative expansion method to derive all of the dimension-6 effective operators, whose coefficients are highly correlated in a specific model.
• We provide bounds to the complete set of dimension-6 operators by including the electroweak precision test and recent Higgs measurements.
• We find that the parameter space of strong first-order phase transitions (induced by the $|H|^6$ operator) can be probed extensively in $Zh$ production at future electron-positron colliders.