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Register a new userHiggs Production in Association with a Dark-Z at Future Electron Positron Colliders
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In recent years there have been many proposals for new electron-positron colliders, such as the Circular Electron-Positron Collider, the International Linear Collider, and the Future Circular Collider in electron-positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the $h,Z$ threshold. However, there are proposals to run these colliders at the lower $WW$ threshold and $Z$-pole energies. In this paper, we propose a new search for Higgs physics accessible at lower energies: $e^+e^-rightarrow h,Z_d$, where $Z_d$ is a new light gauge boson such as a dark photon or dark-$Z$. Such searches can be conducted at the $WW$ threshold, i.e. energies below the $h,Z$ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron-positron colliders, these searches will be sensitive to $Z_d$ masses below 1 GeV, which is lower than the current direct LHC searches. We will show that at $sqrt{s}=160$ GeV with 10 ab$^{-1}$, a search for $e^+e^-rightarrow h,Z_d$ is sensitive to $h-Z-Z_d$ couplings of $deltasim 8times 10^{-3}$ and cross sections of $sim 1-2$ ab for $Z_d$ masses below 1 GeV. The results are similar at $sqrt{s}=240$ GeV with 5 ab$^{-1}$.
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We study associated Higgs production with a photon at electron-positron colliders, $e^+e^-to hgamma$, in various extended Higgs models, such as the inert doublet model (IDM), the inert triplet model (ITM) and the two Higgs doublet model (THDM). The cross section in the standard model (SM) is maximal around $sqrt{s}=$250 GeV, and we present how and how much the new physics can enhance or reduce the production rate. We also discuss the correlation with the $htogammagamma$ and $hto Zgamma$ decay rates. We find that, with a sizable coupling to a SM-like Higgs boson, charged scalars can give considerable contributions to both the production and the decay if their masses are around 100 GeV. Under the theoretical constraints from vacuum stability and perturbative unitarity as well as the current constraints from the Higgs measurements at the LHC, the production rate can be enhanced from the SM prediction at most by a factor of two in the IDM. In the ITM, in addition, we find a particular parameter region where the $hgamma$ production significantly increases by a factor of about six to eight, but the $htogammagamma$ decay still remains as in the SM. In the THDM, possible deviations from the SM prediction are minor in the viable parameter space.
We review the present status of the QCD corrected cross sections and kinematic distributions for the production of a Higgs boson in association with bottom quarks at the Fermilab Tevatron and CERN Large Hadron Collider. Results are presented for the Minimal Supersymmetric Standard Model where, for large tan beta, these production modes can be greatly enhanced compared to the Standard Model case. The next-to-leading order QCD results are much less sensitive to the renormalization and factorization scales than the lowest order results, but have a significant dependence on the choice of the renormalization scheme for the bottom quark Yukawa coupling. We also investigate the uncertainties coming from the Parton Distribution Functions and find that these uncertainties can be comparable to the uncertainties from the remaining scale dependence of the next-to-leading order results. We present results separately for the different final states depending on the number of bottom quarks identified.
Dark sector may couple to the Standard Model via one or more mediator particles. We discuss two types of mediators: the dark photon $A^{prime}$ and the dark scalar mediator $phi$. The total cross-sections and various differential distributions of the processes $e^{+} e^{-} rightarrow q bar{q} A^{prime}$ and $e^{+} e^{-} rightarrow q bar{q} phi$ ($q=u,~d,~c,~s$ and $b$ quarks) are discussed. We focus on the study of the invisible $A^{prime}$ due to the cleaner background at future $e^{+} e^{-}$ colliders. It is found that the kinematic distributions of the two-jet system could be used to identify (or exclude) the dark photon and the dark scalar mediator, as well as to distinguish between them. We further study the possibility of a search for dark photons at a future CEPC experiment with $sqrt{s}=$ 91.2 GeV and 240 GeV. With CEPC running at $sqrt{s}=$ 91.2 GeV, it would be possible to perform a decisive measurement of the dark photon (20 GeV $< m_{A^{prime}} <$ 60 GeV) in less than one operating year. The lower limits of the integrated luminosity for the significance $S/sqrt{B}=$ 2$sigma$, 3$sigma$ and 5$sigma$ are presented.
For the search for additional Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM) as well as for future precision analyses in the Higgs sector a precise knowledge of their production properties is mandatory. We review the evaluation of the cross sections for the neutral Higgs boson production in association with a photon at future $e^+e^-$ colliders in the MSSM with complex parameters (cMSSM). The evaluation is based on a full one-loop calculation of the production mechanism $e^+e^- to h_i gamma$ ($i = 1,2,3$). The dependence of the lightest Higgs-boson production cross sections on the relevant cMSSM parameters is analyzed numerically. We find relatively small numerical depedences of the production cross sections on the underlying parameters.
We investigate the prospects for discovering axion-like particles (ALPs) via a light-by-light (LBL) scattering at two colliders, the future circular collider (FCC-ee) and circular electron-positron collider (CEPC). The protexttt{mi}sing sensitivities to the effective ALP-photon coupling $g_{agammagamma}$ are obtained. Our numerical results show that the FCC-ee and CEPC might be more sensitive to the ALPs with mass 2 GeV $sim$ 10 GeV than the LHC and CLIC.
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