34 research outputs found
Soft-gluon and Coulomb corrections to hadronic top-quark pair production beyond NNLO
We construct a resummation at partial next-to-next-to-next-to-leading
logarithmic accuracy for hadronic top-quark pair production near partonic
threshold, including simultaneously soft-gluon and Coulomb corrections, and use
this result to obtain approximate next-to-next-to-next-to-leading order
predictions for the total top-quark pair-production cross section at the LHC.
We generalize a required one-loop potential in non-relativistic QCD to the
colour-octet case and estimate the remaining unknown two-loop potentials and
three-loop anomalous dimensions. We obtain a moderate correction of
relative to the next-to-next-to-leading order prediction and observe a
reduction of the perturbative uncertainty below .Comment: 47 pages, 5 figures, v2: published version, typos corrected
(including scale uncertainties in Eqs. (4.16)-(4.20)), references added; v3:
see added note on p.30 for changes; the results of this work are implemented
in the program TOPIXS, which can be found at
http://users.ph.tum.de/t31software/topixs
Helicity fractions of W bosons from top quark decays at NNLO in QCD
Decay rates of unpolarized top quarks into longitudinally and transversally
polarized W bosons are calculated to second order in the strong coupling
constant alpha_s. Including the finite bottom quark mass and electroweak
effects, the Standard Model predictions for the W boson helicity fractions are
F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).Comment: 5 pages, 1 figur
Next-to-next-to-leading logarithmic resummation for transverse thrust
We obtain a prediction for the hadron-collider event-shape variable
transverse thrust in which the terms enhanced in the dijet limit are resummed
to next-to-next-to-leading logarithmic accuracy. Our method exploits
universality properties made manifest in the factorized expression for the
cross section and only requires one-loop calculations. The necessary two-loop
ingredients are extracted using known results and existing numerical codes. Our
technique is general and applicable to other observables as well.Comment: 6 pages, 2 figures. v2: Corrected values in Eq.(15); updated Figure 2
accordingl
Higgs effects in top anti-top production near threshold in e+ e- annihilation
The completion of the third-order QCD corrections to the inclusive top-pair
production cross section near threshold demonstrates that the strong dynamics
is under control at the few percent level. In this paper we consider the
effects of the Higgs boson on the cross section and, for the first time,
combine the third-order QCD result with the third-order P-wave, the leading QED
and the leading non-resonant contributions. We study the size of the different
effects and investigate the sensitivity of the cross section to variations of
the top-quark Yukawa coupling due to possible new physics effects.Comment: LaTeX, 17 page
NNLL soft and Coulomb resummation for squark and gluino production at the LHC
We present predictions for the total cross sections for pair production of
squarks and gluinos at the LHC including a combined NNLL resummation of soft
and Coulomb gluon effects. We derive all terms in the NNLO cross section that
are enhanced near the production threshold, which include contributions from
spin-dependent potentials and so-called annihilation corrections. The NNLL
corrections at TeV range from up to for squark-squark
production to for gluino pair production relative to the NLO results and
reduce the theoretical uncertainties of the perturbative calculation to the
level. Grid files with our numerical results are publicly available.Comment: 42 pages, 17 figures. v2: published version; corrected fig. 6;
generalized eq.(A.5) to arbitrary SU(N) gauge group