Echoes of the Electroweak Phase Transition: Discovering a second Higgs doublet through $A_0 \rightarrow H_0 Z$

TL;DR

This paper explores how detecting the decay $A_0 ightarrow H_0 Z$ at the LHC could confirm the existence of a second Higgs doublet, which has implications for cosmology and the matter-antimatter asymmetry.

Contribution

It predicts the scalar spectrum and decay signatures of a second Higgs doublet relevant for electroweak phase transition scenarios and assesses LHC search prospects for these signals.

Findings

Current LHC data may already be sensitive to the $A_0 ightarrow H_0 Z$ decay.

Early 14 TeV runs have high discovery potential for this decay channel.

Observation of this decay would be a key signature of a second Higgs doublet.

Abstract

The existence of a second Higgs doublet in Nature could lead to a cosmological first order electroweak phase transition and explain the origin of the matter-antimatter asymmetry in the Universe. We obtain the spectrum and properties of the new scalars $H_0$, $A_0$ and $H^{\pm}$ that signal such a phase transition, and show that the observation of the decay $A_0 \rightarrow H_0 Z$ at LHC would be a `smoking gun' signature of these scenarios. We analyze the LHC search prospects for this decay in the $\ell \ell b\bar{b}$ and $\ell \ell W^{+} W^{-}$ final states, arguing that current data may be sensitive to this signature in the former channel as well as there being great potential for a discovery in either one at the very early stages of the 14 TeV run.