More Higgses at the LHC and the Electroweak Phase Transition

TL;DR

This paper explores how adding a second Higgs doublet can enable a first order electroweak phase transition, with specific LHC signatures involving new scalar particles, and assesses the prospects for detecting these signatures.

Contribution

It provides detailed properties of new scalars in two-Higgs-doublet models that could facilitate a first order electroweak phase transition and analyzes their LHC detection prospects.

Findings

Decay $A_0 ightarrow H_0 Z$ is a key signature for the phase transition.

LHC search strategies in $ ext{ll}bar{b}$ and $ ext{ll}W^{+}W^{-}$ channels are promising.

Impact on current LHC searches for $A_0$ decaying into SM particles is discussed.

Abstract

A cosmological first order electroweak phase transition could explain the origin of the cosmic matter-antimatter asymmetry. While it does not occur in the Standard Model, it becomes possible in the presence of a second Higgs doublet. In this context, we obtain the properties of the new scalars $H_0$, $A_0$ and $H^{\pm}$ leading to such a phase transition, showing that its key LHC signature would be the decay $A_0 \rightarrow H_0 Z$, and we analyze the promising LHC search prospects for this decay in the $\ell \ell b\bar{b}$ and $\ell \ell W^{+} W^{-}$ final states. Finally, we comment on the impact of the $A_0 \rightarrow H_0 Z$ decay on current LHC searches for $A_0$ decaying into SM particles.