Larbi Rahili

In this paper, pair production of standard model (SM)-like Higgs bosons, h h , is studied through γ γ scattering at future electron-positron colliders, in the framework of the inert doublet model with two active doublets—i.e., the I( 1 + 2 )HDM for short. The relevance of the process γ γ → h h for such a beyond-the-SM (BSM) scenario stems from the fact that it is a one-loop process at lowest order, wherein inert charged states χ ± contribute alongside W ± , H ± , and heavy fermions (primarily, bottom and top quarks), crucially, at the same perturbative order. Given that χ ± / H ± masses and h S + S − ( S ± = χ ± , H ± ) couplings are very mildly constrained, there exist regions of the parameter space of the I ( 1 + 2 ) HDM where the former can be rather light and the latter rather large. After imposing up-to-date theoretical and experimental constraints on the I ( 1 + 2 ) HDM , it is found that the production rates of such processes at future γ γ machines can be enhanced by up to a factor of ≈ 50 with respect to the SM, significantly exceeding typical yields of conventional two-Higgs-doublet models (2HDMs). Further, thanks to the level of control that one can attain at such facilities on the photon kinematics, leading to excellent invariant mass resolution of the incoming photon pairs, we show how it is possible to extract from this process the value of the χ ± mass (along with those of the active H ± states) with high precision, and whichever of the decays of the h h pair, both with and without beam polarization.

Recent experimental hints from the Large Hadron Collider (LHC) in diphoton and partially in the τ + τ − final states suggest the possible existence of an additional Higgs boson with a mass around 95 GeV. Interestingly, these observations are consistent with earlier results from the Large Electron-Positron collider, which pointed to an excess in b b ¯ final states within a similar mass range. Additionally, CMS has observed an excess in the γ γ b b ¯ final state, indicating a possible resonance near 650 GeV decaying into a pair of Standard Model (SM)-like Higgs bosons or into a SM-like Higgs boson accompanied by a lighter scalar with mass near 95 GeV. In this work, we investigate whether these anomalies can be simultaneously explained within the next-to-two-Higgs-doublet model (N2HDM), an extension of the SM scalar sector featuring two complex Higgs doublets and an additional real singlet. Assuming the existence of a C P -even Higgs state compatible with the 95 GeV excesses (restricted to the γ γ and b b ¯ channels), we analyze the Type-II and Type-Y Yukawa structures, taking the observed 650 GeV resonance to be a C P -even Higgs state. An extensive parameter scan is performed, incorporating the latest constraints from the properties of the observed 125 GeV Higgs boson, direct searches for additional Higgs states, flavor physics data, and electroweak precision observables. Our results show that a heavy C P -even Higgs resonance around 650 GeV, produced predominantly via gluon-gluon fusion and subsequently decaying into a 125 GeV Higgs boson together with another scalar at approximately 95 GeV, can be simultaneously accommodated within both the N2HDM Type-II and Type-Y frameworks in parameter regions that remain consistent with the relevant experimental 2 σ intervals for the reported excesses, once all theoretical and experimental constraints are imposed. This interpretation leads to distinctive and testable predictions for the ongoing LHC Run 3 and the forthcoming high-luminosity LHC phase, in particular through correlated rates in the γ γ b b ¯ , τ + τ − b b ¯ , b b ¯ γ γ , and γ γ τ + τ − final states.

In this work, we explore how the 2-Higgs doublet model (2HDM) type-I, extended by an inert doublet, can provide an explanation for the recently observed excesses at the Large Hadron Collider (LHC) in the γ γ and τ + τ − final states. Hence, by imposing theoretical constraints and experimental bounds on the model parameter space, our findings show that a light C P -even Higgs boson, h , with a mass around 95 GeV, can account for these anomalies. This result aligns with the excess in b b ¯ signatures reported in earlier data from the Large Electron-Positron (LEP) collider.

In this study, we propose the interpretation of a 650 GeV excess observed at the Large Hadron Collider (LHC) by the CMS Collaboration in terms of the production of a C P -odd (or pseudoscalar) Higgs boson A , with mass around 650 GeV, decaying into the Standard Model (SM)-like Higgs state h 125 (in turn decaying into γ γ ) and a Z boson (in turn decaying into b b ¯ ), within a three-Higgs doublet model (3HDM) featuring two active and one inert doublet, known as the I ( 1 + 2 ) HDM . This theoretical structure features a spectrum with both the SM-like Higgs boson (with a 125 GeV mass) and a lighter C P -even (or scalar) Higgs state with mass around 95 GeV, h 95 , which is present in this scenario for the purpose of simultaneously explaining anomalies seen in the b b ¯ , γ γ , and τ + τ − final states in searches for additional light Higgs states at the Large Electron-Positron collider and LHC itself. It should be noted that, in the I ( 1 + 2 ) HDM , the inert sector presents loop-induced enhancements to the h 95 → γ γ width via additional scalar charged states, providing a viable mechanism to explain, in particular, the observed (and most significant) diphoton excess at 95 GeV. Taking into account both experimental and theoretical constraints, our results can not only explain the aforementioned anomalies (possibly, aside from the τ + τ − , which is the most marginal one) but also predict, as collateral signals, resonant production of the same C P -odd scalar A followed by the decays: (i) A → h 95 Z , leading to the same γ γ b b ¯ final state displaying the original 650 GeV anomaly and (ii) A → t t ¯ , leading to a well-known and studied signature. Both of these signals are potentially explorable at Run 3 of the LHC and most possibly so at the High-Luminosity LHC, while being consistent with current data at a significance level of 2.5 σ .

We investigate the phenomenology of the charged Higgs boson at the International Linear Collider (ILC) within the framework of the type-X Two-Higgs Doublet Model, where a light charged Higgs boson, with a mass around 200 GeV or even smaller than top quark mass, is still being consistent with flavor physics data as well as with collider experimental data. In the theoretically and experimentally allowed parameter space, the e + e − → H ± W ∓ S (with S = H , A ) production processes can yield signatures with event rates larger than those from e + e − → H + H − and offer sensitivity to the Higgs mixing parameter sin ( β − α ) . We consider the bosonic H ± → W ± S decays, where the neutral scalar S further decays into a pair of tau leptons. We show, through a detector-level Monte Carlo analysis, that the resulting [ τ τ ] [ τ τ ] W W final state could be seen at the ILC with at least 500 GeV center-of-mass energy and 500 fb − 1 of luminosity.

Our goal is to investigate the charged Higgs phenomenology in the framework of 2HDM at the upcoming e + e − and muon colliders. We are primarily concerned with the associated production processes with a fermion pair: ℓ + ℓ − → τ + ν τ H − and ℓ + ℓ − → t b ¯ H − , as well as with the W boson and a neutral Higgs boson: ℓ + ℓ − → W ± H ∓ S ( S = h , H , A ) and ℓ + ℓ − → W ± H ∓ Z . We first update the results for e + e − → { τ + ν τ H − , t b ¯ H − } and then discuss our findings for e + e − → { W ± H ∓ S } for various center-of-mass energies 500 GeV, 1 TeV, 1.5 TeV, and 3 TeV. In the case of muon collider, we show that the new s-channel and t-channel diagrams can increase the cross sections by virtue of their Yukawa couplings. We systematically compare our results for the muon collider with those obtained at the International Linear and Compact Linear colliders. We select benchmark points and conduct signal-background analyses, incorporating detector simulations. For a 3 TeV muon collider, our results show an exclusion region at the 2 σ level and a discovery region at the 5 σ level. Published by the American Physical Society 2024