Next-to-next-to-leading logarithmic threshold resummation for deep-inelastic scattering and the Drell-Yan process

The soft-gluon resummation exponents G^N in moment space are investigated for the quark coefficient functions in deep-inelastic structure functions and the quark-antiquark contribution to the Drell-Yan cross section dsigma/dM. Employing results from two- and three-loop calculations we obtain the next-to-next-to-leading logarithmic terms alpha_s (alpha_s ln N)^n of G^N to all orders in the strong coupling constant alpha_s. These new contributions facilitate a reliable assessment of the numerical effect and the stability of the large-N expansion.Comment: 9 pages, LaTeX, 2 eps-figure

On soft gluon effects in deep-inelastic structure functions

The behaviour of the quark coefficient functions in deep-inelastic scattering is investigated for large values of the Bjorken variable x. By combining results of soft-gluon resummation and fixed-order calculations, we determine the coefficients of the four leading large-x logarithms, alpha_s^k [{ln(1-x)}^{2k-l}/(1-x)]_+, l = 1, ...4, to all orders in the strong coupling constant alpha_s. This result includes two more terms for the three-loop coefficient functions than previously specified in the literature. The effect of the fifth logarithmic contribution is approximately evaluated. The terms derived here are required, but also seem to be sufficient, for a reliable representation of the coefficient functions at large x.Comment: 10 pages, 3 figures, misprints in third line of eq. (15) correcte

Measurement of triple differential photon plus jet cross section by D0

We report on a new measurement of triple differential cross section for the process ppbar -> photon + jet + X in ppbar collisions at sqrt(s)=1.96 TeV by the D0 Collaboration at Fermilab based on a dataset corresponding to an integrated luminosity of 1.1 fb-1.Comment: 3 pages, 1 figure, To appear in the Proceedings of the 2007 Europhysics Conference on High Energy Physics, Manchester, UK. Accepted for publication in Journal of Physics : Conference Serie

A Tree-Loop Duality Relation at Two Loops and Beyond

The duality relation between one-loop integrals and phase-space integrals, developed in a previous work, is extended to higher-order loops. The duality relation is realized by a modification of the customary +i0 prescription of the Feynman propagators, which compensates for the absence of the multiple-cut contributions that appear in the Feynman tree theorem. We rederive the duality theorem at one-loop order in a form that is more suitable for its iterative extension to higher-loop orders. We explicitly show its application to two- and three-loop scalar master integrals, and we discuss the structure of the occurring cuts and the ensuing results in detail.Comment: 20 pages. Few typos corrected, some additional comments included, Appendix B and one reference added. Final version as published in JHE

Approximate NNLO Threshold Resummation in Heavy Flavour Decays

We present an approximate NNLO evaluation of the QCD form factor resumming large logarithmic perturbative contributions in semi-inclusive heavy flavour decays.Comment: 16 pages, 3 figures, Latex; minor changes; 2 figures adde

Phenomenological studies in QCD resummation

We study applications of QCD soft-gluon resummations to electroweak annihilation cross sections. We focus on a formalism that allows to resum logarithmic corrections arising near partonic threshold and at small transverse momentum simultaneously.Comment: 7 pages, LaTeX, 3 figures as eps files. Talk presented by W. Vogelsang at the "XVI International Conference on Particles and Nuclei (PaNic02)", Osaka, Japan, September 200

Threshold resummation for high-transverse-momentum Higgs production at the LHC

We study the resummation of large logarithmic QCD corrections for the process pp ->H+ X when the Higgs boson H is produced at high transverse momentum. The corrections arise near the threshold for partonic reaction and originate from soft gluon emission. We perform the all-order resummation at next-to-leading logarithmic accuracy and match the resummed result with the next-to-leading order perturbative predictions. The effect of resummation on the Higgs transverse momentum distribution at the LHC is discussed.Comment: 19 pages, 3 figure

A New Fracture Function Approach to QCD Initial State Radiation

Ordinary fracture functions, describing hadrons production in the deep inelastic scattering target fragmentation region, are generalized to account for the production of hadrons in arbitrary number, thus offering a renewed framework for dealing with QCD initial state radiation. We also propose a new jet-like observable which measures beam remnants and low-$p_{\perp}$ scattering fragments and derive its QCD evolution equations by using Jet Calculus. Possible implications for semi-inclusive deep inelastic scattering and hadron-hadron reactions are shortly discussed.Comment: 10 pages, 5 figures, revtex

Infrared-Finite Amplitudes for Massless Gauge Theories

We present a method to construct infrared-finite amplitudes for gauge theories with massless fermions. Rather than computing $S$-matrix elements between usual states of the Fock space we construct order-by-order in perturbation theory dressed states that incorporate all long-range interactions. The $S$-matrix elements between these states are shown to be free from soft and collinear singularities. As an explicit example we consider the process $e^+ e^-\to 2$ jets at next-to-leading order in the strong coupling. We verify by explicit calculation that the amplitudes are infrared finite and recover the well-known result for the total cross section $e^+ e^-\to$ hadrons.Comment: 46 page