23,868 research outputs found

### 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

### A Feynman diagram analyzer DIANA: recent development

New developments concerning the extension of the Feynman diagram analyzer
DIANA are presented. We discuss new graphic facilities, application of DIANA to
processes with Majorana fermions and different approaches to automation of
momenta distribution.Comment: 2 pages, Latex using espcrc2.sty, 3 figures using 3 eps files.
Contribution to ACAT 2002, Moscow, Russia, June 24-28, 200

### Highlights of the B-Physics Landscape

The exploration of the quark-flavour sector of the Standard Model is one of
the hot topics in particle physics of this decade. In these studies, which show
a fruitful interplay between theory and experiment, the B-meson system offers a
particularly interesting laboratory. After giving an introduction to
quark-flavour mixing and CP violation as well as to the theoretical tools to
deal with non-leptonic B decays, we discuss popular avenues for new physics to
enter the roadmap of quark-flavour physics. This allows us to have a detailed
look at the B-factory benchmark modes $B^0_d\to J/\psi K_S$, $B^0_d\to \phi
K_S$ and $B^0_d\to\pi^+\pi^-$, with a particular emphasis of the impact of new
physics. We then perform an analysis of the $B\to\pi K$ puzzle, which may
indicate new sources of CP violation in the electroweak penguin sector, and
discuss its implications for rare B and K decays. The next topic is given by
$b\to d$ penguin processes, which are now starting to become accessible at the
B factories, thereby representing a new territory of the B-physics landscape.
Finally, we discuss the prospects for B-decay studies at the Large Hadron
Collider, where the $B^0_s$-meson system plays an outstanding role.Comment: 64 pages, 19 figures, invited topical review for Journal of Physics
G: Nuclear and Particle Physic

### 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

### Sophisticated momenta mapping with DIANA

Details of recent developments of the Feynman diagram analyzer DIANA (DIagram
ANAlyser) are presented. Apart from some discussion about QGRAF and new
plotting features, we concentrate on a new sophisticated mechanism of momenta
mapping.Comment: 4 pages, 4 Encapsulated postscript figures, LaTeX2e, uses espcrc2.sty
(included). Talk given at ACAT0

### 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

### Penguin Topologies, Rescattering Effects and Penguin Hunting with $B_{u,d}\to K\bar{K}$ and $B^\pm\to\pi^\pm K$

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

### New, Efficient and Clean Strategies to Explore CP Violation Through Neutral B Decays

We point out that decays of the kind $B_d\to D_\pm K_{S(L)}$ and $B_s\to
D_\pm\eta^{(')},D_\pm\phi, ...$, where $D_+$ and $D_-$ denote the CP-even and
CP-odd eigenstates of the neutral D-meson system, respectively, provide very
efficient, theoretically clean determinations of the angle $\gamma$ of the
unitarity triangle. In this new strategy, we use the $B^0_q$--$\bar{B^0_q}$
($q\in\{d,s\}$) mixing phase $\phi_q$ as an input, and employ only ``untagged''
and mixing-induced CP-violating observables, which satisfy a very simple
relation, allowing us to determine $\tan\gamma$. Using a plausible dynamical
assumption, $\gamma$ can be fixed in an essentially unambiguous manner. The
corresponding formalism can also be applied to $B_d\to D_\pm\pi^0,D_\pm\rho^0,
>...$ and $B_s\to D_\pm K_{S(L)}$ decays. Although these modes appear less
attractive for the extraction of $\gamma$, they provide interesting
determinations of $\sin\phi_q$. In comparison with the conventional $B_d\to
J/\psi K_{S(L)}$ and $B_s\to J/\psi\phi$ methods, these extractions do not
suffer from any penguin uncertainties, and are theoretically cleaner by one
order of magnitude.Comment: 14 pages, no figures, sign error in factorization prediction for
cos(delta) corrected and numerical examples modified accordingly, conclusions
unchange

### 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

### 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

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