We summarize our recent results on the resummation of hard-scattering coefficient functions and on-shell form factors in massless perturbative QCD. The threshold resummation has been extended to the fourth logarithmic order for deep-inelastic scattering, Drell-Yan lepton pair production and Higgs production via gluon-gluon fusion. The leading six infrared pole terms have been derived to all ord...

We argue that deeply virtual Compton scattering will display Regge behavior ν R(t) at high energy at fixed-t, even at high photon virtuality, not necessarily conventional scaling. A way to see this is to track the Reggeon contributions to quark-nucleon scattering and notice that the resulting Generalized Parton Distributions would have divergent behavior at the break–points. In addition, we sho...

With the advent of quantum chromodynamics as a complete theory of the strong interactions, one can now anticipate understanding the underlying dynamics and composition of both hadrons and nuclei at a fundamental level. In the last few years considerable progress has been made in calculating short distance hadronic scattering and production amplitudes in terms of quark and gluon subprocesses. l-...

We present a model for dihadron fragmentation functions, describing the fragmentation of a quark into two unpolarized hadrons. We tune the parameters of our model to the output of the PYTHIA event generator for two-hadron semi-inclusive production in deep inelastic scattering at HERMES. Once the parameters of the model are fixed, we make predictions for other unknown fragmentation functions and...

We discuss the calculation of two-loop helicity amplitudes for quark-quark scattering in QCD and four-gluino scattering in N = 1 supersymmetric Yang-Mills theory. We study the dependence of the results on different variants of dimensional regularization. In particular, we consider the ’t Hooft-Veltman and four-dimensional helicity (FDH) schemes. We also discuss ambiguities in continuing the Dir...

Parity-violating (PV) interactions among quarks in the nucleon induce a PV γNN coupling, or anapole moment (AM). We compute electroweak gauge-independent contributions to the AM through O(1/Λχ) in chiral perturbation theory. We estimate short-distance PV effects using resonance saturation. The AM contributions to PV electron-proton scattering slightly enhance the axial vector radiative correcti...

We report on a study of the pentaquark Θ+(1540), using a variety of different interpolating fields. We use Chirally Improved fermions in combination with Jacobi smeared quark sources to improve the signal and get reliable results even for small quark masses. The results of our quenched calculations, which have been done on a 123×24 lattice with a lattice spacing of a = 0.148 fm, do not provide ...