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We discuss novel effects in the phenomenology of a light Higgs boson within the context of composite models. We show that large modifications may arise in the decay of a composite Nambu-Goldstone boson Higgs to a photon and a Z boson, h -> Z gamma. These can be generated by the exchange of massive composite states of a strong sector that breaks a left-right symmetry, which we show to be the sole symmetry structure responsible for governing the size of these new effects in the absence of Goldstone-breaking interactions. In this paper we consider corrections to the decay h -> Z gamma obtained either by integrating out vectors at tree level, or by integrating out vector-like fermions at loop level. In each case, the pertinent operators that are generated are parametrically enhanced relative to other interactions that arise at loop level in the Standard Model such as h -> gg and h -> gamma gamma. Thus we emphasize that the effects of interest here provide a unique possibility to probe the dynamics underlying electroweak symmetry breaking, and do not depend on any contrivance stemming from carefully chosen spectra. The effects we discuss naturally lead to concerns of compatibility with precision electroweak measurements, and we show with relevant computations that these corrections can be kept well under control in our general parameter space.
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The significance of new physics appearing in the loop-induced decays of neutral Higgs bosons into pairs of dibosons $gammagamma$ and $Zgamma$ will be discussed in the framework of the 3-3-1 models based on a recent work~cite{Okada:2016whh}, where the Higgs sector becomes effectively the same as that in the two Higgs doublet models (2HDM) after the first symmetry breaking from $SU(3)_L$ scale into the electroweak scale. For large $SU(3)_L$ scale $v_3simeq10$ TeV, dominant one-loop contributions to the two decay amplitudes arise from only the single charged Higgs boson predicted by the 2HDM, leading to that experimental constraint on the signal strength $mu^{331}_{gammagamma}$ of the Standard Model-like Higgs boson decay $hrightarrow gammagamma$ will result in a strict upper bound on the signal strength $mu^{331}_{Zgamma}$ of the decay $hrightarrow, Zgamma$. For a particular model with lower $v_3$ around 3 TeV, contributions from heavy charged gauge and Higgs bosons may have the same order, therefore may give strong destructive or constructive correlations. As a by-product, a deviation from the SM prediction $|mu^{331}_{gammagamma}-1| le 0.04$ still allows $|mu^{331}_{Zgamma}-1|$ to reach values near 0.1. We also show that there exists an $CP$-even neutral Higgs boson $h^0_3$ predicted by the 3-3-1 models, but beyond the 2HDM, has an interesting property that the branching ratio Br$(h^0_3rightarrow gammagamma)$ is very sensitive to the parameter $beta$ used to distinguish different 3-3-1 models.
Higgs boson production in association with a photon ($H$+$gamma$) offers a promising channel to test the Higgs boson to photon coupling at various energy scales. Its potential sensitivity to anomalous couplings of the Higgs boson has not been explored with the proton-proton collision data. In this paper, we reinterpret the latest ATLAS $H$+$gamma$ resonance search results within the Standard Model effective field theory (EFT) framework, using 36.1 fb$^{-1}$ of proton-proton collision data recorded with the ATLAS detector at $sqrt{s}=13$ TeV. Constraints on the Wilson coefficients of dimension-six EFT operators related to the Higgs boson to photon coupling are provided for the first time in the $H$+$gamma$ final state at the LHC.
LHCb will collect large samples of Bd and Bs decays. Combining the CP-violating observables of the decays Bd-->pi+pi- and Bs-->K+K- it is possible to extract the gamma angle of the unitarity triangle. The selection of these decays within the current LHCb simulation framework is outlined and the expected annual event yields and background-to-signal ratios are quoted. Then, the results of a study on the sensitivity that LHCb can achieve for the corresponding CP-violating observables are presented.
The SO(5) x U(1) gauge-Higgs unification in the Randall-Sundrum warped space with the Higgs boson mass m_H=126 GeV is constructed. An universal relation is found between the Kaluza-Klein (KK) mass scale $m_{KK}$ and the Aharonov-Bohm (AB) phase $theta_H$ in the fifth dimension; $m_{KK} sim 1350 GeV/(sin theta_H)^{0.787}$. The cubic and quartic self-couplings of the Higgs boson become smaller than those in the standard model (SM), having universal dependence on $theta_H$. The decay rates H -> gamma gamma, gg are evaluated by summing contributions from KK towers. Corrections coming from KK excited states are finite and about 0.2% (2%) for $theta_H= 0.12 (0.36)$, branching fractions of various decay modes of the Higgs boson remaining nearly the same as in the SM. The signal strengths of the Higgs decay modes relative to the SM are $sim cos^2 theta_H$. The mass of the first KK $Z$ is predicted to be $5.9 (2.4)$TeV for $theta_H= 0.12 (0.36)$. We also point out the possible enhancement of $Gamma(H -> gammagamma)$ due to the large $U(1)_X$ charge of new fermion multiplets.
The new lightest gauge boson $B_H$ with mass of a few hundred GeV is predicted in the littlest Higgs model. $B_H$ should be accessible in the planed ILC and the observation of such particle can strongly support the littlest Higgs model. The realization of $gammagamma$ and $egamma$ collision will open a wider window to probe $B_H$. In this paper, we study the new gauge boson $B_{H}$ production processes $e^{-}gammato e^{-}gamma B_{H}$ and $e^{-}gammato e^{-}Z B_{H}$ at the ILC. Our results show that the production cross section of the process $e^{-}gammato e^{-}Z B_{H}$ is less than one fb in the most parameter spaces while the production cross section of the process $e^{-}gammato e^{-}gamma B_{H}$ can reach the level of tens fb and even hundreds of fb in the sizable parameter spaces allowed by the electroweak precision data. With the high luminosity, the sufficient typical signals could be produced, specially via $e^{-}gammato e^{-}gamma B_{H}$. Because the final electron and photon beams can be easily identified and the signal can be easily distinguished from the background produced by $Z$ and $H$ decaying, $B_H$ should be detectable via $egamma$ collision at the ILC. Therefore, the processes $e^{-}gammato e^{-}gamma B_{H}$ and $e^{-}gammato e^{-}Z B_{H}$ provide a useful way to detect $B_{H}$ and test the littlest Higgs model.
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