A new insight into the phase transition in the early Universe with two Higgs doublets

TL;DR

This paper investigates the electroweak phase transition in the two-Higgs-doublet model, demonstrating the possibility of a strong first-order transition with testable collider signatures, and analyzing the properties of the transition at one-loop level.

Contribution

It provides a detailed analysis of the electroweak phase transition in the 2HDM, including the conditions for a strong first-order transition and potential collider signatures, using one-loop effective potential calculations.

Findings

Strong first-order electroweak phase transition is achievable in 2HDM.

Enhanced triple Higgs coupling is a typical feature of the transition.

Testable collider signatures, including Higgs pair production, are predicted.

Abstract

We study the electroweak phase transition in the alignment limit of the CP-conserving two-Higgs-doublet model (2HDM) of Type I and Type II. The effective potential is evaluated at one-loop, where the thermal potential includes Daisy corrections and is reliably approximated by means of a sum of Bessel functions. Both 1-stage and 2-stage electroweak phase transitions are shown to be possible, depending on the pattern of the vacuum development as the Universe cools down. For the 1-stage case focused on in this paper, we analyze the properties of phase transition and discover that the field value of the electroweak symmetry breaking vacuum at the critical temperature at which the first order phase transition occurs is largely correlated with the vacuum depth of the 1-loop potential at zero temperature. We demonstrate that a strong first order electroweak phase transition (SFOEWPT) in the 2HDM is achievable and establish benchmark scenarios leading to different testable signatures at colliders. In addition, we verify that an enhanced triple Higgs coupling (including loop corrections) is a typical feature of the SFOPT driven by the additional doublet. As a result, SFOEWPT might be able to be probed at the LHC and future lepton colliders through Higgs pair production.