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

TL;DR

This paper investigates how scalar extensions of the Standard Model can induce strong electroweak phase transitions and how future lepton colliders can test these scenarios through precise measurements.

Contribution

It derives the complete set of dimension-6 operators in scalar extension models and assesses their testability at future electron-positron colliders.

Findings

Strong first-order phase transition parameter space can be probed in $Zh$ production.

Electroweak precision tests and Higgs measurements constrain the models.

Future colliders offer extensive sensitivity to the $|H|^6$ operator.

Abstract

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.