Possible indications for new Higgs bosons in the reach of the LHC. N2HDM and NMSSM interpretations

In several searches for additional Higgs bosons at the LHC, in particular in a CMS search exploring decays to pairs of top quarks, $t\overline{t}$, and in an ATLAS search studying tau leptons, τ${}^{+}$τ${}^{-}$, local excesses of about 3 σ standard deviations or above have been observed at a mass scale of approximately 400 GeV . We investigate to what extent a possible signal in these channels could be accommodated in the Next-to-Two-Higgs-Doublet Model (N2HDM) or the Next-to Minimal Supersymmetric Standard Model (NMSSM). In a second step we analyze whether such a model could be compatible with both a signal at around 400 GeV and 96 GeV, where the latter possibility is motivated by observed excesses in searches for the $b\overline{b}$ final state at LEP and the di-photon final state at CMS. The analysis for the N2HDM reveals that the observed excesses at 400 GeV in the $t\overline{t}$ and τ${}^{+}$τ${}^{-}$ channels point towards different regions of the parameter space, while one such excess and an additional Higgs boson at around 96 GeV could simultaneously be accommodated. In the context of the NMSSM an experimental confirmation of a signal in the $t\overline{t}$ final state would favour the alignment-without-decoupling limit of the model, where the Higgs boson at 125 GeV could be essentially indistinguishable from the Higgs boson of the standard model. In contrast, a signal in the τ${}^{+}$τ${}^{-}$ channel can only be accommodated outside of this limit, and parts of the investigated parameter space could be probed with Higgs signal-rate measurements at the (HL-)LHC.