The stringent constraints from the direct searches for exotic scalars at the LHC, as well as indirect bounds from flavor physics measurements, have imposed severe restrictions on the parameter space of new physics models featuring extended Higgs sectors. In the type-II two-Higgs-doublet model (2HDM), this implies a lower bound on the charged Higgs masses of $\mathcal{O}(600\mathrm{GeV})$. In this work we analyze the phenomenology of a $Z_3$ symmetric three-Higgs-doublet model in the alignment limit focusing on the impact of flavor physics constraints on its parameter space. We show that the couplings of the two charged Higgs bosons in this model feature an additional suppression factor compared to type-II 2HDM. This gives rise to a significant relaxation of the flavor physics constraints in this model, allowing the charged Higgs masses to be as low as $\mathcal{O}(200\mathrm{GeV})$. We also consider the constraints coming from precision electroweak observables and the observed diphoton decay rate of the 125 GeV Higgs boson at the LHC. The bounds coming from the direct searches of nonstandard Higgs bosons at the LHC, particularly those from resonance searches in the ditau channel, prove to be very effective in constraining this scenario further.

• Received 21 April 2021
• Accepted 30 September 2021

DOI:https://doi.org/10.1103/PhysRevD.104.075033

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Published by the American Physical Society