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Large perturbative corrections, which appear in perturbative expressions for many QCD observables, either at small QT or at partonic threshold, can be organized by way of all order resummation. Joint resummation allows simultaneous resummation of threshold and recoil effects and its impact has been assessed upto leading log, next-to-leading log (NLL) and in some cases up to NNLL accuracy. We discuss another class of terms, called soft-collinear effects, which give rise to corrections of the form lnj N / N and their impact on the joint resummed calculations of prompt photon production cross section.

We introduce a notion of position-space cuts of eikonal diagrams, the set of diagrams appearing in the perturbative expansion of the correlator of a set of straight semi-infinite Wilson lines. The cuts are applied directly to the position-space representation of any such diagram and compute its imaginary part to the leading order in the dimensional regulator. Our cutting prescription thus defines a position-space analog of the standard momentum-space Cutkosky rules. Unlike momentum-space cuts which put internal lines on shell, position-space cuts constrain a number of the gauge bosons exchanged between the energetic partons to be lightlike, leading to a vanishing and a non-vanishing imaginary part for space- and timelike kinematics, respectively., Comment: 5 pages, 2 figures; minor changes; version published in PRL

We further develop the formalism for taking position-space cuts of eikonal diagrams introduced in ref. [1]. These cuts are applied directly to the position-space representation of any such diagram and compute its discontinuity to the leading order in the dimensional regulator. We provide algorithms for computing the position-space cuts and apply them to several two- and three-loop eikonal diagrams, finding agreement with results previously obtained in the literature. We discuss a non-trivial interplay between the cutting prescription and non-Abelian exponentiation. We furthermore discuss the relation of the imaginary part of the cusp anomalous dimension to the static interquark potential., Journal of High Energy Physics, 2015 (7), ISSN:1126-6708, ISSN:1029-8479

This is a summary of theoretical progress presented at TOP2013. I review new results and methods in producing top quarks singly, in pairs or in association with other particles and/or jets, in addition to special aspects of its production like the forward-backward asymmetry. The role of top in certain New Physics models was discussed, as well as the careful definition of its mass. The emergent picture is one of impressive progress on the theoretical front of top quark physics., Proc. of Top 2013, 108 - 122; DESY-PROC-2014-02; ISSN 1435-8077

Open heavy flavour production at $e^+e^-$ colliders in deeply inelastic $e\gamma$ scattering has an interesting feature: the structure function $F_2(x,Q^2)$ for this process is calculable for $x>0.01$, and is essentially proportional to the gluon density in the photon for smaller $x$ values. We give estimates for event rates at LEP2 and a Next Linear Collider in $x,Q^2$ bins, and present differential distributions in the transverse momentum and rapidity of the heavy quark for the case of charm. We include all next-to-leading-order QCD corrections, and find theoretical uncertainties are well under control.

We develop a method for computing Mellin moments of single inclusive cross sections such as Drell-Yan production directly from forward scattering diagrams, by invoking unitarity in the form of cutting equations. We provide a diagram-independent prescription for eliminating contributions from unwanted cuts at the level of an expansion in the reciprocal omega=1/z variable. The modified sum over powers of omega produces the result from physical cuts only, with the nth coefficient precisely equal to the nth Mellin moment of the cross section. We demonstrate and validate our method for representative one- and two-loop diagrams., Comment: 37 pages with 13 figures

We extend next-to-leading logarithmic threshold and joint resummation for prompt photon production to include leading collinear effects. The impact of these effects is assessed for both fixed-target and collider kinematics. We find them in general to be small, but noticeable., Comment: 14 pages, 12 figures, added comment on fragmentation contribution and one more reference. Version to appear in Phys. Rev. D

We review the production of charm and bottom quarks in two-photon collisions at e+e- colliders. The next-to-leading order QCD predictions for total cross sections and differential distributions are compared with recent experimental results., 6 pages, 2 figures. Talk given at the UK Phenomenology Workshop on Collider Physics, Durham, England, 19-24 Sep 1999

I present a short overview of the NLO QCD calculations available for deep-inelastic production of heavy quarks., 3 pages. Talk given at UK Phenomenology Workshop on Collider Physics, Durham, England, 19-24 Sep 1999

We extend the phase space slicing method of Giele, Glover and Kosower for performing next-to-leading order jet cross section calculations in two important ways: we show how to include fragmentation functions and how to include massive particles. These extensions allow the application of this method to not just jet cross sections but also to cross sections in which a particular final state particle, including a $D$ or $B$-meson, is tagged., 36 pages, Latex Small corrections to text. To appear in Phys. Rev. D

We present the threshold resummation for the cross section for electroproduction of heavy quarks. We work to next-to-leading logarithmic accuracy, and in single-particle inclusive kinematics. We provide next-to-leading and next-to-next-to-leading order expansions of our resummed formula, and examine numerically the quality of these finite order approximations. For the case of charm we study their impact on the structure function $F_2$ and its differential distribution with respect to the charm transverse momentum., 27 pages, 17 figures

We examine the contributions of soft gluons to the Higgs production cross section at the LHC in the Standard Model and its minimal supersymmetric extension. The soft gluon radiation effects of this reaction share many features with the Drell-Yan process, but arise at lowest order from a purely gluonic initial state. We provide an extension of the conventional soft gluon resummation formalism to include a new class of contributions which we argue to be universal, and resum these and the usual Sudakov effects to all orders. The effect of these new terms is striking: only if they are included, does the expansion of the resummed cross section to next-to-leading order reproduce the exact result to within a few percent for the full range of Higgs boson masses. We use our resummed cross section to derive next-to-next-to-leading order results, and their scale dependence. Moreover, we demonstrate the importance of including the novel contributions in the resummed Drell-Yan process., Comment: LaTeX, 28 pages, 12 figures. Some formulae modified; main results and figures unchanged

The next-to-leading order QCD corrections to the production of a $W$-boson in association with a jet containing a heavy quark are presented. The calculation is fully differential in the final state particle momenta and includes the mass of the heavy quark. We study for the case of the Tevatron the sensitivity of the cross section to the strange quark distribution function, the dependence of the cross section on the heavy quark mass, the transverse momentum distribution of the jet containing the heavy quark, and the momentum distribution of the heavy quark in the jet., 12 pages, Latex, epsfig, 7 figures appended as uuencode file

In two-photon collisions at LEP2 and a future $e^+e^-$ linear collider heavy quarks (mainly charm) will be pair-produced rather copiously. The production via direct and resolved photons can be distinguished experimentally via a remnant-jet tag. We study correlations of the heavy quarks at next-to-leading order in QCD in the direct channel, which is free from phenomenological parton densities in the photon. These correlations are therefore directly calculable in perturbative QCD and provide a stringent test of the production mechanism., Comment: 10 pages, LaTeX, epsfig, 5 figures appended as uuencoded file (hardcopy can be obtained upon request from mkraemer@desy.de or laenen@surya11.cern.ch)

It has been observed that in the DIS scheme the refactorization of the Drell-Yan cross section leading to exponentiation of threshold logarithms can also be used to organize a class of constant terms, most of which arise from the ratio of the timelike Sudakov form factor to its spacelike counterpart. We extend this exponentiation to include all constant terms, and demonstrate how a similar organization may be achieved in the MSbar scheme. We study the relevance of these exponentiations in a two-loop analysis., 20 pages, JHEP style, no figures

We exhibit a method for simultaneously treating recoil and threshold corrections in single-photon inclusive cross sections, working within the formalism of collinear factorization. This approach conserves both the energy and transverse momentum of resummed radiation. At moderate p_T, we find the potential for substantial enhancements from higher-order perturbative and power-law nonperturbative corrections., 9 Pages, LaTeX, two figures as eps files