Double real radiation corrections to gluon scattering at NNLO

We use the antenna subtraction method to isolate the double real radiation infrared singularities present in the six-gluon tree-level process at next-to-next-to-leading order. We show numerically that the subtraction term correctly approximates the matrix elements in the various single and double unresolved configurations.Comment: six pages, talk given at 10th DESY Workshop on Elementary Particle Theory, Worlitz, 25-30 April 201

Infrared structure of e+e−→3e^+e^- \to 3 jets at NNLO: QED-type contributions

The NNLO QCD corrections to the $e^+e^- \to 3$ jets can be decomposed according to their colour factors. Out of the seven colour factors, three are of QED-type: $1/N^2$, $N_F/N$ and $N_F^2$. We use the antenna subtraction method to compute these contributions, providing complete expressions for the subtraction terms in $N_F/N$ and $N_F^2$.Comment: Talk presented at Loops and Legs 2006, Eisenac

The sector decomposition approach to real radiation at NNLO

A method based on sector decomposition is briefly described which is suitable for the calculation of the double real radiation part of e^+e^- to 3 jets at next-to-next-to-leading order in a fully differential way.Comment: 5 pages, 2 figures, to appear in the proceedings of the 7th International Symposium on Radiative Corrections (RADCOR05), Shonan Village, Japan, 200

Two-Loop Quark and Gluon Form Factors in Dimensional Regularisation

We compute the two-loop corrections to the massless quark form factor $\gamma^* \to q\bar q$ and gluon form factor $H\to gg$ to all orders in the dimensional regularisation parameter $\epsilon=(4-d)/2$. The two-loop contributions to the form factors are reduced to linear combinations of master integrals, which are computed in a closed form, expressed as $\Gamma$-functions and generalised hypergeometric functions of unit argument. Using the newly developed HypExp-package, these can be expanded to any desired order, yielding Laurent expansions in $\epsilon$. We provide expansions of the form factors to order $\epsilon^2$, as required for ultraviolet renormalisation and infrared factorisation of the three-loop form factors.Comment: 9 pages, latex, references update

Light fermionic NNLO QCD corrections to top-antitop production in the quark-antiquark channel

We present the NNLO corrections to top pair production in the quark-antiquark channel proportional to the number of light quark flavors $N_l$. While the double real corrections were derived previously, here we compute the real-virtual and virtual-virtual contributions in this partonic channel. Using the antenna subtraction formalism, we show that the subtraction terms correctly approximate the real-virtual contributions in all their infrared limits. Combined with the integrated forms of the double real and real-virtual subtraction terms, we show analytically that the explicit infrared poles cancel at the real-virtual and virtual-virtual levels respectively, thereby demonstrating the validity of the massive extension of the NNLO antenna formalism. These NNLO corrections are implemented in a Monte Carlo parton level generator providing full kinematical information on an event-by event basis. With this program, NNLO differential distributions in the form of binned histograms are obtained and presented here.Comment: 42 pages, 8 figure

Radiative corrections to the photon + 1 jet rate at LEP

We present a complete calculation of the photon +1 jet rate in e(^+)e(^-) annihilation up to O(aa(_s)). Although formally of next-to-leading order in perturbation theory, this calculation contains several ingredients appropriate to a next-to-next-to-leading order calculation of jet observables. No such calculation has been performed before, and the work discussed here represents a first step in that direction. In particular, we describe a generalization of the commonly used phase space slicing method to isolate the singularities present when more than one particle is unresolved. More precisely, we provide an analytic evaluation of the following multiple unresolved factors: triple collinear factor, soft/collinear factor and double single collinear factor. By comparing the results of our calculation with the existing data on the photon +1 jet rate from the ALEPH Collaboration at CERN, we make a new determination of the process-independent non-perturbative quark-to-photon fragmentation function D(_q-γ)(z,μ(_F)) at O(aa(_s)). at As a first application of this measurement allied with our improved perturbative calculation, we determine the dependence of the isolated photon -fl jet cross section in a democratic clustering approach on the jet resolution parameter y(_cut) at next-to-leading order. Inclusion of the next-to-leading order corrections to this observable considerably improves the agreement between theoretical prediction and experimental data

e^+ e^- -> 3 jets and event shapes at NNLO

We report on the calculation of NNLO corrections to the 3-jet cross section and related event shape distributions in electron-positron annihilation. The corrections are sizable for all variables, however the magnitude of the corrections is substantially different for different observables. We observe that inclusion of the NNLO corrections yields a considerably better agreement between theory and experimental data both in shape and normalization of the event shape distributions in the region where the perturbative result is expected to hold. A new extraction of $\alpha_{s}$ using the event shape variables up to NNLO yields a considerably better consistency between the observables indicating a stabilization of the perturbative corrections at this order.Comment: Contribution to the Proceedings of the 9th DESY workshop on "Loops and Legs in Quantum Field Theory", Sondershausen, April 200