Status of jet cross sections to NNLO

I review the state-of-the-art for fully differential numerical NNLO programs. Topics which are covered include the calculation of two-loop amplitudes, multiple polylogarithms, cancellation of infra-red divergences at NNLO and the efficient generation of the phase space. Numerical results for e+ e- --> 2 jets are also discussed.Comment: 5 pages, to appear in the proceedings of the conference "Loops and Legs", Eisenach, 200

HypExp, a Mathematica package for expanding hypergeometric functions around integer-valued parameters

We present the Mathematica package HypExp which allows to expand hypergeometric functions $_JF_{J-1}$ around integer parameters to arbitrary order. At this, we apply two methods, the first one being based on an integral representation, the second one on the nested sums approach. The expansion works for both symbolic argument $z$ and unit argument. We also implemented new classes of integrals that appear in the first method and that are, in part, yet unknown to Mathematica.Comment: 33 pages, latex, 2 figures, the package can be downloaded from http://krone.physik.unizh.ch/~maitreda/HypExp/, minor changes, works now under Window

On Demand, Development and Dependence: A Review of Current and Future Implications of Socioeconomic Changes for Integrated Water Resource Management in the Okavango Catchment of Southern Africa

Water is both a key and limited resource in the Okavango Catchment of Southern Africa. It is vital for the ecosystem and the three riparian states Angola, Botswana and Namibia who use the water of the catchment for multiple purposes including pastoralism, farming and tourism. Socioeconomic changes, primarily strong population growth and increasing development demands pose significant challenges for the Okavango Catchment and its Integrated Water Resource Management (IWRM). In this paper, we first review the socioeconomic background and the current and projected water situation. Against this background, we analyze the dependence of the riparian states and the local livelihoods on the Okavango Catchment. Third, we discuss the implications of socioeconomic changes and increased water demand for the IWRM in the catchment. We review the scientific literature and relevant reports. Further we utilize (geo-spatial) analysis of socioeconomic, livelihood and hydrological data, supplemented by a field visit to Namibia and Botswana. Our findings suggest that strong population growth and the stabilization of Angola are likely to increase the pressure to develop the region along the Okavango. The central challenge for IWRM is hence to enable Angola to meet its development needs without limiting livelihood and economic prospects in Botswana and Namibia

Subtraction terms for one-loop amplitudes with one unresolved parton

Fully differential next-to-next-to-leading order calculations require a method to cancel infrared singularities. In a previous publication, I discussed the general setup for the subtraction method at NNLO. In this paper I give all subtraction terms for electron-positron annihilation associated with one-loop amplitudes with one unresolved parton. These subtraction terms are integrated within dimensional regularization over the unresolved one-particle phase space. The results can be used with all variants of dimensional regularization (conventional dimensional regularization, the 't Hooft-Veltman scheme and the four-dimensional scheme).Comment: 27 page

SFC-based Communication Metadata Encoding for Adaptive Mesh

This volume of the series “Advances in Parallel Computing” contains the proceedings of the International Conference on Parallel Programming – ParCo 2013 – held from 10 to 13 September 2013 in Garching, Germany. The conference was hosted by the Technische Universität München (Department of Informatics) and the Leibniz Supercomputing Centre.The present paper studies two adaptive mesh refinement (AMR) codes whose grids rely on recursive subdivison in combination with space-filling curves (SFCs). A non-overlapping domain decomposition based upon these SFCs yields several well-known advantageous properties with respect to communication demands, balancing, and partition connectivity. However, the administration of the meta data, i.e. to track which partitions exchange data in which cardinality, is nontrivial due to the SFC’s fractal meandering and the dynamic adaptivity. We introduce an analysed tree grammar for the meta data that restricts it without loss of information hierarchically along the subdivision tree and applies run length encoding. Hence, its meta data memory footprint is very small, and it can be computed and maintained on-the-fly even for permanently changing grids. It facilitates a forkjoin pattern for shared data parallelism. And it facilitates replicated data parallelism tackling latency and bandwidth constraints respectively due to communication in the background and reduces memory requirements by avoiding adjacency information stored per element. We demonstrate this at hands of shared and distributed parallelized domain decompositions.This work was supported by the German Research Foundation (DFG) as part of the Transregional Collaborative Research Centre “Invasive Computing (SFB/TR 89). It is partially based on work supported by Award No. UK-c0020, made by the King Abdullah University of Science and Technology (KAUST)

Fully differential QCD corrections to single top quark final states

A new next-to-leading order Monte Carlo program for calculation of fully differential single top quark final states is described and first results presented. Both the s- and t-channel contributions are included.Comment: 3 pages, 3 figures, talk presented at DPF2000, August 9-12, 2000. To appear in International Journal of Modern Physics

- XSummer - Transcendental Functions and Symbolic Summation in Form

Harmonic sums and their generalizations are extremely useful in the evaluation of higher-order perturbative corrections in quantum field theory. Of particular interest have been the so-called nested sums,where the harmonic sums and their generalizations appear as building blocks, originating for example from the expansion of generalized hypergeometric functions around integer values of the parameters. In this Letter we discuss the implementation of several algorithms to solve these sums by algebraic means, using the computer algebra system Form.Comment: 21 pages, 1 figure, Late

One-loop N-point equivalence among negative-dimensional, Mellin-Barnes and Feynman parametrization approaches to Feynman integrals

We show that at one-loop order, negative-dimensional, Mellin-Barnes' (MB) and Feynman parametrization (FP) approaches to Feynman loop integrals calculations are equivalent. Starting with a generating functional, for two and then for $N$-point scalar integrals we show how to reobtain MB results, using negative-dimensional and FP techniques. The $N-$point result is valid for different masses, arbitrary exponents of propagators and dimension.Comment: 11 pages, LaTeX. To be published in J.Phys.

Expansion around half-integer values, binomial sums and inverse binomial sums

I consider the expansion of transcendental functions in a small parameter around rational numbers. This includes in particular the expansion around half-integer values. I present algorithms which are suitable for an implementation within a symbolic computer algebra system. The method is an extension of the technique of nested sums. The algorithms allow in addition the evaluation of binomial sums, inverse binomial sums and generalizations thereof.Comment: 21 page

NLO QCD corrections to t tbar + jet production at hadron colliders

We report on the calculation of the next-to-leading order QCD corrections to the production of top--anti-top quark pairs in association with a hard jet at the Tevatron and at the LHC. We present results for the t tbar + jet cross section and the forward--backward charge asymmetry. The corrections stabilize the leading-order prediction for the cross section. The charge asymmetry receives large corrections.Comment: 4 page