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Register a new userGauge-Higgs unification at $e^+ e^-$ linear colliders
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Authors
Yutaka Hosotani
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In gauge-Higgs unification the 4D Higgs boson appears as a part of the fifth dimensional component of gauge potentials, namely as a fluctuation mode of the Aharonov-Bohm phase in the extra dimension. The $SO(5) times U(1) times SU(3)$ gauge-Higgs unification gives nearly the same phenomenology as the standard model (SM) at low energies. It predicts KK excited states of photon, $Z $ boson, and $Z_R$ boson ($Z$ bosons) around 7 - 8 TeV. Quarks and leptons couple to these $Z$ bosons with large parity violation, which leads to distinct interference effects in $e^+ e^- rightarrow mu^+ mu^-, q , bar q$ processes. At 250 GeV ILC with polarized electron beams, deviation from SM can be seen at the 3 - 5 sigma level even with 250 fb$^{-1}$ data, namely in the early stage of ILC. Signals become stronger at higher energies. Precision measurements of interference effects at electron-positron colliders at energies above 250 GeV become very important to explore physics beyond the standard model.
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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.
% insert abstract here We study the production of the Higgs bosons predicted in the Minimal Supersymmetric extension of the Standard Model $(h^0, H^0, A^0, H^pm)$, with the reactions $e^{+}e^{-}to bbar b h^0 (H^0, A^0)$, and $e^+e^-to tau^-bar u_tau H^+, tau^+ u_tau H^-$, using the helicity formalism. We evaluate cross section of $h^0, H^0, A^0$ and $H^pm$ in the limit when $tanbeta$ is large. The numerical computation is done considering two stages of a possible Next Linear $e^{+}e^{-}$ Collider: the first with $sqrt{s}=500$ $GeV$ and design luminosity 50 $fb^{-1}$, and the second with $sqrt{s}=1$ $TeV$ and luminosity 100-200 $fb^{-1}$.
It is generally accepted that experiments at an e+e- linear colliders will be able to extract the masses of the selectron as well as the associated sneutrinos with a precision of ~ 1% by determining the kinematic end points of the energy spectrum of daughter electrons produced in their two body decays to a lighter neutralino or chargino. Recently, it has been suggested that by studying the energy dependence of the cross section near the production threshold, this precision can be improved by an order of magnitude, assuming an integrated luminosity of 100 fb^-1. It is further suggested that these threshold scans also allow the masses of even the heavier second and third generation sleptons and sneutrinos to be determined to better than 0.5%. We re-examine the prospects for determining sneutrino masses. We find that the cross sections for the second and third generation sneutrinos are too small for a threshold scan to be useful. An additional complication arises because the cross section for sneutrino pair to decay into any visible final state(s) necessarily depends on an unknown branching fraction, so that the overall normalization in unknown. This reduces the precision with which the sneutrino mass can be extracted. We propose a different strategy to optimize the extraction of m(tilde{ u}_mu) and m(tilde{ u}_tau) via the energy dependence of the cross section. We find that even with an integrated luminosity of 500 fb^-1, these can be determined with a precision no better than several percent at the 90% CL. We also examine the measurement of m(tilde{ u}_e) and show that it can be extracted with a precision of about 0.5% (0.2%) with an integrated luminosity of 120 fb^-1 (500 fb^-1).
We study the Higgs pair-production in the Standard Model of the strong and electroweak interactions at future $e^{+}e^{-}$ collider energies, with the reaction $e^{+}e^{-}to t bar t HH$. We evaluated the total cross section of $tbar tHH$ and calculate the number total of events considering the complete set of Feynman diagrams at tree-level. The numerical computation is done for the energy which is expected to be available at a possible Next Linear $e^{+}e^{-}$ Collider: with center-of-mass energy $800, 1600$ $GeV$ and luminosity 1000 $fb^{-1}$.
We analyse the loop induced production of Higgs boson pairs at future high--energy $e^+e^-$ colliders, both in the Standard Model and in its minimal supersymmetric extension. The cross sections for Standard Model Higgs pair production through $W/Z$ boson loops, $ee ra H^0 H^0$, are rather small but the process could be visible for high enough luminosities, especially if longitudinal polarization is made available. In the Minimal Supersymmetric Standard Model, the corresponding processes of CP--even or CP--odd Higgs boson pair production, $ee ra hh, HH, Hh$ and $ee ra AA$ have smaller cross sections, in general. The additional contributions from chargino/neutralino and slepton loops are at the level of a few percent in most of the supersymmetric parameter space.
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