The new particles are predicted by Beyond the Standard Model theories that can explain the baryon-antibaryon asymmetry of the universe (BAU), one of the holy grails of modern fundamental physics. We focus on the unexplored asymmetric Higgs decay X->SH , where X and S denote two BSM spin-0 Higgs-like neutral particles while H denotes the already experimentally known Higgs boson. The existence of several new Higgs-like spin-0 particles is perfectly compatible with state-of-the-art Higgs precision physics and leads to dramatic experimental signatures. Asymmetric Higgs decays are present in most BSM Higgs extensions.

The goals of this project are:

1. a) Utilize the ATLAS Run-2 and Run-3 data to search for additional spin-0 Higgs particles in the very characteristic and low background final state with two b-quarks and two photons.
2. Interpretation of the experimental results in the framework of complete models and synergy with primordial Gravitational Wave (GW) searches. Populations of models that can be probed both with HL-LHC projected data and future space-based GW telescopes such as LISA will be identified, and models relevant to primordial GW excluded by our full Run-3 will be identified.