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Register a new userTesting Higgs Self-Couplings at High-Energy Linear Colliders
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M.M. Muhlleitner
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In order to verify the Higgs mechanism experimentally, the Higgs self-couplings have to be probed. These couplings allow the reconstruction of the characteristic Higgs potential responsible for the electroweak symmetry breaking. The couplings are accessible in a variety of multiple Higgs production processes. The theoretical analysis including the most relevant channels for the production of neutral Higgs boson pairs at high-energy and high-luminosity $e^+e^-$ linear colliders will be presented in this note.
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Standard Model Higgs pair production at e^+e^- colliders has the capability to determine the Higgs boson self-coupling lambda. I present a detailed analysis of the e^+e^- -> ZHH and e^+e^- -> ubar u HH signal channels, and the relevant background processes, for future e^+e^- linear colliders with center of mass energies of sqrt{s}=0.5 TeV, 1 TeV, and 3 TeV. Special attention is given to the role non-resonant Feynman diagrams play, and the theoretical uncertainties of signal and background cross sections. I also derive quantitative sensitivity limits for lambda. I find that an e^+e^- collider with sqrt{s}=0.5 TeV can place meaningful bounds on lambda only if the Higgs boson mass is relatively close to its current lower limit. At an e^+e^- collider with sqrt{s}=1 TeV (3 TeV), lambda can be determined with a precision of 20-80% (10-20%) for integrated luminosities in the few ab^{-1} range and Higgs boson masses in the range m_H=120-180 GeV.
The $h(125)$ boson, discovered only in 2012, is lower than the top quark in mass, hence $t to ch$ search commenced immediately thereafter, with current limits at the per mille level and improving. As the $t to ch$ rate vanishes with the $h$-$H$ mixing angle $cosgamma to 0$, we briefly review the collider probes of the top changing $tcH/tcA$ coupling $rho_{tc}$ of the exotic $CP$-even/odd Higgs bosons $H/A$. Together with an extra top conserving $ttH/ttA$ coupling $rho_{tt}$, one has an enhanced $cbH^+$ coupling alongside the familiar $tbH^+$ coupling, where $H^+$ is the charged Higgs boson. The main processes we advocate are $cg to tH/A to ttbar c,; ttbar t$ (same-sign top and triple-top), and $cg to bH^+ to btbar b$. We also discuss some related processes such as $cg to thh$, $tZH$ that depend on $cosgamma$ being nonzero, comment briefly on $gg to H/A to tbar t, tbar c$ resonant production, and touch upon the $rho_{tu}$ coupling.
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We discuss the testability of CP-violating phases at future lepton colliders for the scenario which satisfies electric dipole moment data by destructive interferences among several phases. We consider the general but aligned two Higgs doublet model which has the CP-violating phases in the Higgs potential and the Yukawa interaction. The Yukawa interaction terms are aligned to avoid flavor changing neutral currents at tree level. The Higgs potential is also aligned such that the coupling constants of the lightest Higgs boson with the mass of 125 GeV to the Standard Model (SM) particles are the same as those of the SM at tree level. We investigate the azimuthal angle distribution of the hadronic decay of tau leptons arising from production and decay of the extra Higgs bosons, which contains information of the CP-violating phases. From the signal and background simulation, we find that the scenario with finite CP-violating phases can be distinguished from CP conserving one at future lepton colliders like the International Linear Collider.
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