Electroweak production of light scalar-pseudoscalar pairs from extended Higgs sectors

Understand

In models with extended Higgs sectors, it is possible that the Higgs boson discovered at the LHC is not the lightest one.

• We show that in a realistic model (the Type I 2-Higgs Doublet Model), when the sum of the masses of a light scalar and a pseudoscalar ($h$ and $A$) is smaller than the $Z$ boson mass, the Electroweak (EW) production of an $hA$ pair can dominate over QCD production by orders of magnitude, a fact not previously highlighted.
• This is because in the $gg$-initiated process, $hA$ production via a resonant $Z$ in the $s$-channel is prohibited according to the Landau-Yang theorem, which is not the case for the $q\bar{q}$-initiated process.
• We explore the parameter space of the model to highlight regions giving such $hA$ solutions while being consistent with all constraints from collider searches, $b$-physics and EW precision data.