855 research outputs found

    About helicity conservation in gauge boson scattering at high energy

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    We remark that the high energy gauge boson scattering processes involving two-body initial and final states, satisfy certain selection rules described as helicity conservation of the \underline{gauge boson} amplitudes (GBHC). These rules are valid at Born level, as well as at the level of the leading and sub-leading 1-loop logarithmic corrections, in both the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). A "fermionic equivalence" theorem is also proved, which suggests that GBHC is valid at all orders in MSSM at sufficiently high energies, where the mass suppressed contributions are neglected.Comment: 7 pages, 2 figures, version to appear in Phys. Rev. Letter

    The processes of gluon fusion producing chargino or neutralino pairs at high energies

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    According to the helicity conservation (HCns) theorem, the sum of the helicities should be conserved, in any 2-to-2 processes in MSSM with R-parity conservation, at high energies; i.e. all amplitudes violating this rule, must vanish asymptotically. The realization of HCns in gluon-fusion to charginos or neutralinos is studied, at the one loop electroweak order (EW), and simple high energy expressions are derived for the non-vanishing helicity conserving (HC) amplitudes. These are very similar to the corresponding expressions for ggW+W,ZZ,γZ,γγgg \to W^+W^-, ZZ, \gamma Z, \gamma\gamma derived before. Asymptotic relations among observable unpolarized cross sections for many such processes are then obtained, some of which may hold at LHC-type energies.Comment: Extended version to appear in International Journal of Modern Physics A 21 page

    Studying Trilinear Gauge Couplings at Linear Collider Energies

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    We study the sensitivity of the processes `e+ e- -> lepton (l) neutrino (v) quark (u) antiquark (d)', where the lepton is an electron or a muon, on the non-standard trilinear gauge couplings (TGC), using the optimal observables method at Linear Collider energies. Our study is based on the four-fermion generator ERATO. Taking into account all possible correlations between the different trilinear gauge coupling parameters, we show that they can be measured with an accuracy of 10310^{-3} to 10410^{-4} for typical Linear Collider energies and luminosities.Comment: 17 pages, LaTeX, version to appear in Zeitschrift fur Physi

    The Higgs boson structure functions as signposts of new physics

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    We show that the Higgs boson structure functions observable in the inclusive process ee+H+"anything"e^-e^+ \to H + {\rm "anything"} may reveal the presence of anomalous contributions corresponding to several types of new physics partners, Higgs boson compositeness or invisible (dark) matter. This could be done without making a difficult or even an impossible experimental analysis of the contents of the "anything". We give illustrations showing how the shapes of the various structure functions containing such typical new contributions may differ from the standard prediction and allow their identification.Comment: 19 pages, 36 figures, version accepted in Phys. Rev.

    A supersimple analysis of ee+ttˉe^-e^+\to t \bar t at high energy

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    According to supersimplicity in MSSM, a renormalization scheme (SRS) may be defined for any high energy 2-to-2 process, to the 1loop EW order; where the helicity conserving (HC) amplitudes, are expressed as a linear combination of just three universal logarithm-involving forms. All other helicity amplitudes vanish asymptotically. Including to these SRS amplitudes the corresponding counter terms, the "supersimple" expressions for the high energy HC amplitudes, renormalized on-shell, are obtained. Previously, this property was noted for a large number of processes that do not involve Yukawa interactions or renormalization group corrections. Here we extend it to ee+ttˉe^-e^+\to t \bar t, which does involve large Yukawa and renormalization group contributions. We show that the resulting "supersimple" expressions may provide an accurate description, even at energies comparable to the SUSY scale. Such descriptions clearly identify the origin of the important SUSY effects, and they may be used for quickly constraining physics contributions, beyond MSSM.Comment: 26 pages, 15 figures. Paper appeared in Phys. Rev. D. The Journal where Reference 20 has appeared has been adde

    The γγA0A0\gamma \gamma \to A^0 A^0 process at a γγ\gamma \gamma Collider

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    The helicity amplitudes for the process γγA0A0\gamma \gamma \to A^0 A^0 are studied to 1-loop order in the minimal SUSY (MSSM) model, where A0A^0 is the CP-odd Higgs particle. Simple exact analytic formulae are obtained, in terms of the C0C_0 and D0D_0 Passarino-Veltman functions; in spite of the fact that the loop-diagrams often involve different particles running along their sides. For a usual mSUGRA set of parameters, σ(γγA0A0)(0.10.2)fb\sigma (\gamma \gamma \to A^0 A^0) \sim (0.1-0.2)\rm fb is expected. If SUSY is realized in Nature, these expressions should be useful for understanding the Higgs sector.Comment: Misprints in typos corrected, 1 reference added e-mail: [email protected]

    Higgs boson form factor effects in ttˉt\bar t production by WW+W^-W^+ and ZZZZ fusion

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    We study the fusion processes WW+ttˉW^-W^+\to t\bar t and ZZttˉZZ\to t\bar t observable at a future ee+e^-e^+ collider and we discuss their sensitivity to an HttHtt form factor which may be due to compositeness, in particular when the HH and the top quark have common constituents. We make an amplitude analysis and illustrate which helicity amplitudes and cross sections for specific final ttˉt\bar t polarizations are especially sensitive to this form factor.Comment: 24 pages, 37 figures, version including changes suggested by the Physical Review D publication tea
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