DIANA and selected applications

New developments concerning the extension of the Feynman diagram analyzer DIANA are presented. We discuss new graphics facilities, different approaches to automation of momenta distribution and parallel processing facilities. Furthermore applications to $t\bar t$ production and Bhabha scattering are shortly discussed.Comment: Latex, 5 pages, 4 eps figures, uses included npb.sty, presented by at RADCOR and Loops and Legs 2002 8-13 September 2002, in Kloster Banz, German

Calculation of Feynman diagrams with zero mass threshold from their small momentum expansion

A method of calculating Feynman diagrams from their small momentum expansion [1] is extended to diagrams with zero mass thresholds. We start from the asymptotic expansion in large masses [2] (applied to the case when all $M_i^2$ are large compared to all momenta squared). Using dimensional regularization, a finite result is obtained in terms of powers of logarithms (describing the zero-threshold singularity) times power series in the momentum squared. Surprisingly, these latter ones represent functions, which not only have the expected physical `second threshold' but have a branchcut singularity as well below threshold at a mirror position. These can be understood as pseudothresholds corresponding to solutions of the Landau equations. In the spacelike region the imaginary parts from the various contributions cancel. For the two-loop examples with one mass $M$, in the timelike region for $q^2 \approx M^2$ we obtain approximations of high precision. This will be of relevance in particular for the calculation of the decay $Z \to b\bar{b}$ in the $m_b=0$ approximation.Comment: 17 pages with figures and tables, PostScript file gzip'ed and uuencode

Steps towards full two-loop calculations for 2 fermion to 2 fermion processes: running versus pole masses schemes

Recent progress in the calculation of the two-loop on-shell mass counterterms within the electroweak Standard Model (SM) for the massive particles are discussed. We are in progress of developing a package for full two-loop SM calculations of 2 -> 2 fermion processes, with emphasis on the analytical approach where feasible. The complete two-loop on-shell renormalization is implemented. Substantial progress has been made in calculating the master integrals. We are able to compute in an efficient and stable manner up to a few thousands of diagrams of very complex mass structure.Comment: 4 pages, 1 style file. To appear in the proceedings of 9th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 03), Tsukuba, Japan, 1-5 Dec 200

Parallel Computation of Feynman diagrams with DIANA

Co-operation of the Feynman DIagram ANAlyzer (DIANA) with the underlying operational system (UNIX) is presented. We discuss operators to run external commands and a recent development of parallel processing facilities and an extension in the spirit of a component model.Comment: 23 pages, Latex using psfig, epsf and alltt, 3 figure

Some methods to evaluate complicated Feynman integrals

I discuss a progress in calculations of Feynman integrals based on the Gegenbauer Polynomial Technique and the Differential Equation Method.Comment: 2 pages, 1 figure, latex. Talk presented at the 8th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2002), Moscow, Russia, June 200

CP Violation and the Role of Electroweak Penguins in Non-leptonic B Decays

The phenomenon of CP violation in the B system and strategies for extracting CKM phases are reviewed. We focus both on general aspects and on some recent developments including CP-violating asymmetries in B_d decays, the B_s system in light of a possible width difference $\Delta\Gamma_s$, charged B decays, and SU(3) relations among certain transition amplitudes. In order to describe the relevant non-leptonic B decays, low energy effective Hamiltonians calculated beyond the leading logarithmic approximation are used. Special emphasis is given to the role of electroweak penguin operators in such transitions. These effects are analyzed both within a general framework and more specifically in view of the theoretical cleanliness of methods to determine CKM phases. Strategies for obtaining insights into the world of electroweak penguins are discussed.Comment: Invited review article for publication in International Journal of Modern Physics A. 62 pages, LaTeX, 16 figures. The complete paper is also available via anonymous ftp at ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints

Theoretical Review of CP Violation

The focus of our considerations is the B-meson system, which will provide stringent tests of the Kobayashi-Maskawa mechanism of CP violation in this decade. After a classification of the main possible strategies to achieve this goal, we discuss the status of the B-factory benchmark modes in view of the current experimental data. We shall then turn to the "El Dorado" for B-decay studies at hadron colliders, the Bs-meson system, where we will also address new, theoretically clean strategies to explore CP violation.Comment: 10 pages, 3 figures, invited talk at the International Workshop on QCD: QCD@Work 2003 - Conversano (Italy) 14-18 June 2003 (eConf C030614

Penguin Topologies, Rescattering Effects and Penguin Hunting with Bu,d→KKˉB_{u,d}\to K\bar{K} and B±→π±KB^\pm\to\pi^\pm K

In the recent literature, constraints on the CKM angle $\gamma$ arising from the branching ratios for $B^\pm\to\pi^\pm K$ and $B_d\to\pi^\mp K^\pm$ decays received a lot of attention. An important theoretical limitation of the accuracy of these bounds is due to rescattering effects, such as $B^+\to\{\pi^0K^+\}\to\pi^+K^0$. We point out that these processes are related to penguin topologies with internal up quark exchanges and derive SU(2) isospin relations among the $B^+\to\pi^+K^0$ and $B_d^0\to\pi^-K^+$ decay amplitudes by defining ``tree'' and ``penguin'' amplitudes in a proper way, allowing the derivation of generalized bounds on the CKM angle $\gamma$. We propose strategies to obtain insights into the dynamics of penguin processes with the help of the decays $B_{u,d}\to K\bar{K}$ and $B^\pm\to\pi^\pm K$, derive a relation among the direct CP-violating asymmetries arising in these modes, and emphasize that rescattering effects can be included in the generalized bounds on $\gamma$ completely this way. Moreover, we have a brief look at the impact of new physics.Comment: Some mistakes in the equations have been corrected, conclusions have been changed slightly. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/, or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints