Abstract
We study the production of a Higgs boson recoiling from a massless invisible system in e + e − collisions. This is a quite distinctive signature that can arise when the Higgs boson is produced in association with a massless dark photon, which can happen in BSM scenarios foreseeing an extra unbroken U(1) gauge group. Dark photons can indeed acquire effective couplings to the Higgs boson as occurs in models recently proposed to generate exponentially-spread Yukawa couplings. We analyze the signal and corresponding backgrounds for $$ H\to b\overline{b} $$ , and estimate ILC and FCC-ee sensitivities in a model-independent way.
Highlights
In this connection, in [12] a new paradigm has been proposed to generate exponentiallyspread Yukawa couplings from gauge quantum numbers in the dark sector
This is a quite distinctive signature that can arise when the Higgs boson is produced in association with a massless dark photon, which can happen in BSM scenarios foreseeing an extra unbroken U(1) gauge group
The resulting chiral-symmetry and Flavor breaking in the dark sector is transferred to the Yukawa-coupling sector at one-loop via scalar messenger fields that are charged under both SM and U(1)F gauge interactions
Summary
We introduce the dark-photon effective couplings to the Higgs boson that enter the e+e− → Hγcross section. In order to express the coefficients Cγγ, CZγ, Cγγin eq (2.2) in terms of the fundamental parameters of the model, one can match the tree-level widths, based on the parametrization in eq (2.2), for the Higgs decays H → γγ, H → Zγ, H → γγ, respectively, with the corresponding one-loop results computed in the full model (as sketched in figure 3) This will be discussed, after introducing a particular NP framework. The Mmiss spectrum of the signal and background processes are compared, after applying PYTHIA showering, jet reconstruction and jet-energy resolution effects on top of parton-level simulation (right panel). Jet reconstruction and energy-resolution effects (as in the right panel of the figure) degrades the Mmiss spectrum of the signal quite a lot, shifting the peak away from zero and smearing it. The latter match sensitivities on the corresponding BR(H → γγ) and BR(H → Zγ) that are smaller than the FCC-ee ones by an order of magnitude
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