Infrared Scales and Factorization in QCD

Effective field theory methods are used to study factorization of the deep inelastic scattering cross-section. The cross-section is shown to factor in QCD, even though it does not factor in perturbation theory for some choices of the infrared regulator. Messenger modes are not required in soft-collinear effective theory for deep inelastic scattering as x -> 1.Comment: 5 pages, 2 figures, revtex

Top-Quark Pair Production Beyond Next-to-Leading Order

We report on recent calculations of the differential cross section for top-quark pair production at hadron colliders. The results are differential with respect to the top-pair invariant mass and to the partonic scattering angle. In these calculations, which were carried out by employing soft-collinear effective theory techniques, we resummed threshold logarithms up to next-to-next-to-leading logarithmic order. Starting from the differential cross section, it is possible to obtain theoretical predictions for the invariant-mass distribution and the total cross section. We summarize here our results for these observables, and we compare them with the results obtained from different calculational methods.Comment: Talk presented at Loops and Legs in Quantum Field Theory 2010, Woerlitz, Germany, April 25-30, 2010. 6 page

RG-improved single-particle inclusive cross sections and forward-backward asymmetry in ttˉt\bar t production at hadron colliders

We use techniques from soft-collinear effective theory (SCET) to derive renormalization-group improved predictions for single-particle inclusive (1PI) observables in top-quark pair production at hadron colliders. In particular, we study the top-quark transverse-momentum and rapidity distributions, the forward-backward asymmetry at the Tevatron, and the total cross section at NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed order. We also perform a detailed analysis of power corrections to the leading terms in the threshold expansion of the partonic hard-scattering kernels. We conclude that, although the threshold expansion in 1PI kinematics is susceptible to numerically significant power corrections, its predictions for the total cross section are in good agreement with those obtained by integrating the top-pair invariant-mass distribution in pair invariant-mass kinematics, as long as a certain set of subleading terms appearing naturally within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table