41 research outputs found
Azimuthal angular dependence of decay lepton in e+ e- --> t tbar
We discuss top quark production and its subsequent decay for searching new
physics at lepton colliders. The angular dependence of the decay leptons is
calculated including both QCD corrections and anomalous gamma Z - t tbar
couplings. The off-diagonal spin basis for the top and anti-top quarks is shown
to be useful to probe the anomalous couplings.Comment: 12 pages, LaTeX, 9 ps figure
On enhanced corrections from quasi-degenerate states to heavy quarkonium observables
It is well known that in perturbation theory existence of quasi-degenerate
states can rearrange the order counting. For a heavy quarkonium system,
naively, enhanced effects (-changing mixing effects) could contribute
already to the first-order and third-order corrections to the wave function and
the energy level, respectively, in expansion in . We present a
formulation and note that the corresponding (lowest-order) corrections vanish
due to absence of the relevant off-diagonal matrix elements. As a result, in
the quarkonium energy level and leptonic decay width, the enhanced effects are
expected to appear, respectively, in the fifth- and fourth-order corrections
and beyond.Comment: 9 page
Determination of and from quarkonium 1S energy levels in perturbative QCD
We update determination of the masses of the charm and
bottom quarks, from comparisons of the masses of the charmonium and bottomonium
states with their perturbative predictions up to
next-to-next-to-next-to-leading order in expansion and using the
masses. Effects of non-zero charm-quark mass in the
bottomonium masses are incorporated up to next-to-next-to-leading order. We
obtain and , which agree with the current Particle
Data Group values.Comment: 12 pages, 5 figures, 1 table. v2: Typo corrected in Eq.(3); no change
of final result
The real photon structure functions in massive parton model in NLO
We investigate the one-gluon-exchange () corrections to the
real photon structure functions , , and
in the massive parton model.
We employ a technique based on the Cutkosky rules and the reduction of
Feynman integrals to master integrals. We show that a positivity constraint,
which is derived from the Cauchy-Schwarz inequality, is satisfied among the
unpolarized and polarized structure functions , and
calculated up to the next-to-leading order in QCD.Comment: arXiv admin note: text overlap with arXiv:1110.262