Two-Loop Ultrasoft Running of the O(v^2) QCD Quark Potentials

The two-loop ultrasoft contributions to the next-to-leading logarithmic (NLL) running of the QCD potentials at order v^2 are determined. The results represent an important step towards the next-to-next-to-leading logarithmic (NNLL) description of heavy quark pair production and annihilation close to threshold.Comment: 13 pages, 3 figures; typos corrected, reference added, information on cross checks added on page 7; acknowledgments adde

Light Quark Mass Effects in Bottom Quark Mass Determinations

Recent results for charm quark mass effects in perturbative bottom quark mass determinations from $\Upsilon$ mesons are reviewed. The connection between the behavior of light quark mass corrections and the infrared sensitivity of some bottom quark mass definitions is examined in some detail.Comment: Invited talk presented at RADCOR-2000, Carmel, CA, Sep. 2000; 15 pages, latex, 3 postscript figures; eliminated typo in Eq.(3

Top Quark Pair Production at Threshold -- Uncertainties and Relativistic Corrections

It is shown how nonrelativistic QCD (NRQCD) can be used to determine next-to-next-to-leading order relativistic and short-distance contributions to the total $t\bar t$ production cross section in the threshold regime at lepton colliders. A recipe for the calculation of all such contributions for the total photon mediated production cross section is presented and a review of the already known Abelian next-to-next-to-leading results is given.Comment: Talk presented at the Workshop on Physics at the First Muon Collider and the Front End of a Muon Collider, Fermilab, November 6-9, 1997, to appear in the proceedings; 9 pages, latex, one ps figure include

Summing Logs of the Velocity in NRQCD and Top Threshold Physics

To achieve reliable predictions of the top-antitop threshold cross section at a future e+e- Linear Collider logarithms of the top velocity need to be resummed. I review the issues that make this problem complicated and show how the task can be achieved by renormalization in an effective theory using the so called velocity renormalization group. The most recent NNLL order results are discussed.Comment: 12 pages, uses ws-procs9x6.cls and rotating_pr.sty, 2 ps figures. Invited talk at Continuous Advances in QCD 2004, Minneapolis, USA, May 13-16,200

Top Physics at Threshold and Beyond

A review on theoretical aspects of top quark physics at the Linear Collider is given with focus on the process $e^+e^-\to t\bar t$ and the presentations given at this conference.Comment: 8 pages, latex (sprocl_my.sty), 2 postscript figures. Plenary talk presented at The Worldwide Study on Physics and Experiments with Future Linear e+e- Colliders, Sitges, Spain, April 28 - May 5 199

Non-Relativistic Effective Field Theory for Perturbative Heavy Quark--Antiquark Systems

Recent developments for an effective theory for non-relativistic perturbative quark-antiquark systems are reviewed and some applications are discussed.Comment: 15 pages, latex (sprocl.sty), 2 postscript figures. Invited talk presented at the 5th Workshop on QCD (QCD 2000), Villefranche-sur-Mer, France, 3-7 Jan 200

Top Pair Production at Threshold and Effective Theories

I give an introduction to the effective field theory description of top pair production at threshold in e+e- annihilation. The impact of the summation of logarithms of the top quark velocity including most recent results at next-to-next-to-leading logarithmic order is discussed.Comment: 19 pages, appolb_mod.cls, 4 postscript figures. Invited plenary talk at Cracow Epiphany Conference on Heavy Flavors, January 3-6, 200

Three-Loop Anomalous Dimension of the Heavy Quark Pair Production Current in Non-Relativistic QCD

The three-loop non-mixing contributions to the anomalous dimension of the leading order quark pair production current in non-relativistic QCD are computed. It is demonstrated that the renormalization procedure can only be carried out consistently if the dynamics of both soft and the ultrasoft degrees of freedom is present for all scales below the heavy quark mass, and if the soft and ultrasoft renormalization scales are always correlated.Comment: 19 pages, revtex, 5 postscript figures include