We study the enhancement of the di-Higgs production cross section resulting from the resonant decay of a heavy Higgs boson at hadron colliders in a model with a Higgs singlet. This enhancement of the double Higgs production rate is crucial in understanding the structure of the scalar potential and we determine the maximum allowed enhancement such that the electroweak minimum is a global minimum. The di-Higgs production enhancement can be as large as a factor of ~ 18 (13) for the mass of the heavy Higgs around 270 (420) GeV relative to the Standard Model rate at 14 TeV for parameters corresponding to a global electroweak minimum.
Higgs pair production at the LHC from gluon fusion is small in the Standard Model, but can be enhanced in models where a resonant enhancement is allowed. We examine the effect of a resonant contribution from a second scalar arising in a model with a gauge singlet scalar field in addition to the usual SU(2) scalar doublet, with mass up to $M_H$~600 GeV and discuss the interference effects in double Higgs production. We compute the NLO QCD corrections in the large $m_t$ limit and show that they can significantly distort kinematic distributions near the resonance peak.
We investigate the prospective reach of the 14 TeV HL-LHC for resonant production of a heavy Higgs boson that decays to two SM-like Higgs bosons in the $4b$ final state in the scalar singlet extended Standard Model. We focus on the reach for choices of parameters yielding a strong first order electroweak phase transition. The event selection follows the $4b$ analysis by the ATLAS Collaboration, enhanced with the use of a boosted decision tree method to optimize the discrimination between signal and background events. The output of the multivariate discriminant is used directly in the statistical analysis. The prospective reach of the $4b$ channel is compatible with previous projections for the $bbgammagamma$ and $4tau$ channels for heavy Higgs boson mass $m_2$ below 500 GeV and superior to these channels for $m_2 > 500$ GeV. With 3 ab$^{-1}$ of integrated luminosity, it is possible to discover the heavy Higgs boson in the $4b$ channel for $m_2< 500$ GeV in regions of parameter space yielding a strong first order electroweak phase transition and satisfying all other phenomenological constraints.
A coupling of a scalar, charged under an unbroken global U(1) symmetry, to the Standard Model via the Higgs portal is one of the simplest gateways to a dark sector. Yet, for masses $m_{S}geq m_{H}/2$ there are few probes of such an interaction. In this note we evaluate the sensitivity to the Higgs portal coupling of di-Higgs boson production at the LHC as well as at a future high energy hadron collider, FCC-hh, taking into account the full momentum dependence of the process. This significantly impacts the sensitivity compared to estimates of changes in the Higgs-coupling based on the effective potential. We also compare our findings to precision single Higgs boson probes such as the cross section for vector boson associated Higgs production at a future lepton collider, e.g. FCC-ee, as well as searches for missing energy based signatures.
We consider extended scalar sectors of the Standard Model as ultraviolet-complete motivations for studying the effective Higgs self-interaction operators of the Standard Model effective field theory. We investigate all motivated heavy scalar models which generate the dimension-6 effective operator, $|H|^6$, at tree level and proceed to identify the full set of tree-level dimension-six operators by integrating out the heavy scalars. Of seven models which generate $|H|^6$ at tree level only two, quadruplets of hypercharge $Y=3Y_H$ and $Y=Y_H$, generate only this operator. Next we perform global fits to constrain relevant Wilson coefficients from the LHC single Higgs measurements as well as the electroweak oblique parameters $S$ and $T$. We find that the $T$ parameter puts very strong constraints on the Wilson coefficient of the $|H|^6$ operator in the triplet and quadruplet models, while the singlet and doublet models could still have Higgs self-couplings which deviate significantly from the standard model prediction. To determine the extent to which the $|H|^6$ operator could be constrained, we study the dihiggs signatures at the future 100 TeV collider and explore future sensitivity of this operator. Projected onto the Higgs potential parameters of the extended scalar sectors, with $3$ ab$^{-1}$ luminosity data we will be able to explore the Higgs potential parameters in all seven models.
We analyse the consequences of the little Higgs model for double Higgs boson production at the LHC and for the partial decay width of the Higgs into two photons. In particular, we study the sensitivity of these processes in terms of the parameters of the model. We find that the little Higgs model contributions are proportional to (v/f)^4 and hence do not change significantly either single or double Higgs production at hadron colliders or the partial decay width of the Higgs into two photons as compared to the standard model predictions. However, when interference and mixing effects are properly taken into account these contributions increase to be of the order of (v/f)^2.