22 research outputs found
Finite-width effects in the near-threshold ZZZ and ZWW production at ILC
We calculate the cross-section of the near-threshold off-shell and
production at the International Linear Collider taking into account
their instability and the principal part of NLO corrections. The calculations
are performed in the framework of the model of unstable particles with smeared
mass-shell. We show that the contribution of the finite and widths
(their instability) is large in the Higgs resonance range and should be taken
into account in the Higgs boson searches at future colliders.Comment: 5 pages, 6 figure
Bjorken Sum Rule and pQCD frontier on the move
The reasonableness of the use of perturbative QCD notions in the region close
to the scale of hadronization, i.e., below \lesssim 1 \GeV is under study.
First, the interplay between higher orders of pQCD expansion and higher twist
contributions in the analysis of recent Jefferson Lab (JLab) data on the
Generalized Bjorken Sum Rule function at is studied. It is shown that the inclusion of the higher-order
pQCD corrections could be absorbed, with good numerical accuracy, by change of
the normalization of the higher-twist terms. Second, to avoid the issue of
unphysical singularity (Landau pole at Q=\Lambda\sim 400 \MeV ), we deal with
the ghost-free Analytic Perturbation Theory (APT) that recently proved to be an
intriguing candidate for a quantitative description of light quarkonia spectra
within the Bethe-Salpeter approach. The values of the twist coefficients
extracted from the mentioned data by using the APT approach provide
a better convergence of the higher-twist series than with the common pQCD. As
the main result, a good quantitative description of the JLab data down to
350 MeV is achieved.Comment: 10 pages, 3 figures, minor change
All one-loop scalar vertices in the effective potential approach
Using the one-loop Coleman-Weinberg effective potential, we derive a general analytic expression for all the derivatives of the effective potential with respect to any number of classical scalar fields. The result is valid for a renormalisable theory in four dimensions with any number of scalars, fermions or gauge bosons. This result corresponds to the zero-external momentum contribution to a general one-loop diagram with N scalar external legs. We illustrate the use of the general result in two simple scalar singlet extensions of the Standard Model, to obtain the dominant contributions to the triple couplings of light scalar particles under the zero external momentum approximation
Central Exclusive \chi_c Production
The amplitudes of the central exclusive production of c mesons are calculated using different unintegrated gluon distribution functions (UGDFs). The procedure of generalisation of UGDF for non-forward case by saturation of positivity constraints is suggested. We compare exclusive production of all charmonium states c(0+), c(1+) and c(2+) including branching fraction for radiative J/ + decay channel. Kinematical enhancement of the maximal helicity amplitudes is shown