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  • 2000-2004  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 19 (2001), S. 57-76 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. If the standard model (SM) Higgs particle is sufficiently heavy, then its contribution to $\gamma \gamma \to Z Z$ should be largely imaginary, interfering with the also predominantly imaginary SM “background” generated by the W loop. For standard model Higgs masses in the region $200\lesssim m_H \lesssim 500$ GeV, this interference is found to be constructive and increasing the Higgs signal. In the minimal SUSY case an interference effect should also appear for the contribution of the heavier CP-even neutral Higgs boson $H^0$ , provided it is sufficiently heavy. The effect is somewhat reduced, though, by the smallness of the $H^0$ width and the $\gamma\gamma$ and ZZ branching ratios. The interference is again found to be constructive for part of the parameter space corresponding to sfermion masses at the TeV scale and maximal stop mixing. For both the SM and the SUSY case, regions of the parameter space exist, though, where the interference may be destructive. It is therefore essential to take these effects into account when searching for possible scalar Higgs-like candidates. To this aim, we present the complete analytic expressions for both resonance and background amplitudes.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We study the helicity amplitudes of the process $\gamma \gamma \to Z Z$ in the Standard Model at high energy. These amplitudes receive contributions from the W and charged quark and lepton loops, analogous to those encountered in the $\gamma \gamma \to \gamma\gamma, \gamma Z$ cases studied before. But $\gamma \gamma \to ZZ$ also receives contributions from the Higgs s-channel poles involving the effective Higgs- $\gamma \gamma$ vertex. At energies $\gsim 300 GeV$ , the amplitudes in all three processes are mainly helicity-conserving and almost purely imaginary; which renders them a very useful tool in searching for New Physics. As an example, a SUSY case is studied, and the signatures due to the virtual effects induced by a chargino-, charged slepton- or a lightest stop-loop in $\gamma \gamma \to ZZ$ , are explored. These signatures, combined with the analogous ones in $\gamma \gamma \to \gamma \gamma$ and $\gamma \gamma \to \gamma Z$ , should help identifying the nature of possible New Physics particles.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 20 (2001), S. 659-675 
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The process $\gamma\gamma\to ZH$ first arises at the one loop level, and as such it provides us with remarkable tests of the structure of the electroweak Higgs sector. These tests are complementary to those in the gauge sector involving $\gamma\gamma\to \gamma\gamma, \gamma Z, ZZ$ . We show that in the standard model (SM) where $H=H_{\mathrm{{SM}}}$ , as well as in the supersymmetric case where $H=h^0, H^0$ or $A^0$ , observables exist (like e.g. the energy dependence, angular distribution, photon polarization dependence or final Z polarization) which present rather spectacular properties. Such properties involve strong threshold effects with steps, bumps or peaks, reflecting the type of Higgs and heavy quarks and chargino masses and couplings predicted by the SM and supersymmetric models.
    Type of Medium: Electronic Resource
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