855 research outputs found

### About helicity conservation in gauge boson scattering at high energy

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

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 $gg \to
W^+W^-, ZZ, \gamma Z, \gamma\gamma$ 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

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 $10^{-3}$ to $10^{-4}$ 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

We show that the Higgs boson structure functions observable in the inclusive
process $e^-e^+ \to H + {\rm "anything"}$ 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 $e^-e^+\to t \bar t$ at high energy

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 $e^-e^+\to t \bar t$, 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 $\gamma \gamma \to A^0 A^0$ process at a $\gamma \gamma$ Collider

The helicity amplitudes for the process $\gamma \gamma \to A^0 A^0$ are
studied to 1-loop order in the minimal SUSY (MSSM) model, where $A^0$ is the
CP-odd Higgs particle.
Simple exact analytic formulae are obtained, in terms of the $C_0$ and $D_0$
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, $\sigma (\gamma \gamma \to A^0 A^0) \sim (0.1-0.2)\rm fb$ 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 $t\bar t$ production by $W^-W^+$ and $ZZ$ fusion

We study the fusion processes $W^-W^+\to t\bar t$ and $ZZ\to t\bar t$
observable at a future $e^-e^+$ collider and we discuss their sensitivity to an
$Htt$ form factor which may be due to compositeness, in particular when the $H$
and the top quark have common constituents. We make an amplitude analysis and
illustrate which helicity amplitudes and cross sections for specific final
$t\bar t$ 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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