Two Higgs doublets, Effective Interactions and a Strong First-Order Electroweak Phase Transition

TL;DR

This paper explores how extending the Higgs potential with dimension-6 operators can enable a strong first-order electroweak phase transition in 2HDMs, with implications for collider phenomenology and Higgs pair production.

Contribution

It identifies specific Higgs potential extensions via effective field theory that facilitate a strong phase transition and analyzes their phenomenological signatures at the LHC.

Findings

Certain dimension-6 operators enable a strong first-order phase transition.

Higgs pair production and interference effects are key signatures for 2HDM exotics.

The reliability of the dimension-6 approximation depends on the specific 2HDM phenomenology.

Abstract

It is well-known that type II two Higgs doublet models (2HDMs) can struggle to facilitate a strong first-order electroweak phase transition in the early universe whilst remaining theoretically appealing scenarios for many reasons. We analyse this apparent shortfall from the perspective of additional new physics. Starting from a consistent dimension-6 effective field theory Higgs potential extension, we identify the Higgs potential extensions that provide the necessary additional contributions required to achieve a strong first-order electroweak phase transition and trace their phenomenological implications for the Large Hadron Collider. In passing, we critically assess the reliability of the dimension-6 approximation depending on the expected 2HDM phenomenology. In particular, we focus on the role of Higgs pair production (resonant and non-resonant) and interference effects expected in top final states, which are the prime candidates of 2HDM exotics discoveries.