624 research outputs found
NNNLO correction to the toponium and bottomonium wave-functions at the origin
We report new results of the NNNLO correction to the S-wave quarkonium
wave-functions at the origin, which also provide an estimate of the resonance
cross section in t-tbar threshold production at the ILC.Comment: 5 pages, 2 figures, Proceedings of 2007 International Linear Collider
Workshop: LCWS07 and ILC07, Hamburg, Germany, 30 May - 3 Jun 200
Spin Dependence of Heavy Quarkonium Production and Annihilation Rates: Complete Next-to-Next-to-Leading Logarithmic result
The ratio of the photon mediated production or annihilation rates of spin
triplet and spin singlet heavy quarkonium states is computed to the
next-to-next-to-leading logarithmic accuracy within the nonrelativistic
renormalization group approach. The result is presented in analytical form and
applied to the phenomenology of , and systems.
The use of the nonrelativistic renormalization group considerably improves the
behaviour of the perturbative expansion and is crucial for accurate theoretical
analysis. For bottomonium decays we predict . Our results question the
accuracy of the existing extractions of the strong coupling constant from the
bottomonium annihilation. As a by-product we obtain novel corrections to the
ratio of the ortho- and parapositronium decay rates: the corrections of order
and .Comment: Appendices A.4, A.5 and B correcte
High Order QED Corrections in Physics of Positronium
High-order perturbative corrections to positronium decays and hyperfine
splitting are briefly reviewed. Theoretical predictions are compared to the
most recent experimental data. Perspectives of future calculations are
discussed.Comment: 8 pages, LaTeX, talk given at Workshop on Positronium Physics, ETH
Honggerberg, Zurich, May 30-31, 2003, a misprint in Eq. (1) correcte
Ultrasoft contribution to quarkonium production and annihilation
We compute the third-order correction to electromagnetic
S-wave quarkonium production and annihilation rates due to the emission and
absorption of an ultrasoft gluon. Our result completes the analysis of the
non-relativistic quarkonium bound-state dynamics in the
next-to-next-to-next-to-leading order. The impact of the ultrasoft correction
on the Upsilon(1S) leptonic width and the top quark-antiquark threshold
production cross section is estimated.Comment: 10 page
Splitting from Nonrelativistic Renormalization Group
We compute the hyperfine splitting in a heavy quarkonium composed of
different flavors in next-to-leading logarithmic approximation using the
nonrelativistic renormalization group. We predict the mass difference of the
vector and pseudoscalar charm-bottom mesons to be MeV.Comment: Eq.(22) and Appendix corrected, numerical results slightly changed.
arXiv admin note: text overlap with arXiv:hep-ph/031208
Trace anomalies and the rule
Trace Anomaly Dominance in weak -decays successfully reproduces the
selection rule results, as observed in and .Comment: 10 pages, no figur
Fermionic Corrections to the Three-Loop Matching Coefficient of the Vector Current
In this paper we consider the matching coefficient of the vector current
between Quantum Chromodynamics (QCD) and Non-Relativistic QCD (NRQCD) to
three-loop order in perturbation theory. We evaluate the fermionic corrections
containing a closed massless fermion loop. The results are building blocks both
for the bottom and top quark system at threshold. We explain in detail the
methods used for the evaluation of the Feynman diagrams, classify the occurring
master integrals and provide results for the latter. The numerical effects are
significant. They have the tendency to improve the behaviour of the
perturbative series -- both for the bottom and top quark system.Comment: 21 page
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