Echoes of the Electroweak Phase Transition: Discovering a second Higgs doublet through $A_0\to H_{0}Z$

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 $\mathrm{\ell }\mathrm{\ell }b\bar{b}$ 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.