The Pythia program can be used to generate high-energy-physics ''events'', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.

/pdf/pythia-6-4-physics-and-manual-3dvwmijpnq.pdf

PYTHIA 6.4 Physics and Manual

http://risa.stanford.edu/teaching/362/particledarkmatter.pdf

Particle dark matter: Evidence, candidates and constraints

This paper gives the 2010 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. The 2010 adjustment takes into account the data considered in the 2006 adjustment as well as the data that became available from 1 January 2007, after the closing date of that adjustment, until 31 December 2010, the closing date of the new adjustment. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2010 set replaces the previously recommended 2006 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.

/pdf/codata-recommended-values-of-the-fundamental-physical-4bsdant71c.pdf

CODATA Recommended Values of the Fundamental Physical Constants: 2006

Theory and phenomenology of two-Higgs-doublet models

We review the present status of QCD corrections to weak decays beyond the leading-logarithmic approximation, including particle-antiparticle mixing and rare and $\mathrm{CP}$-violating decays. After presenting the basic formalism for these calculations we discuss in detail the effective Hamiltonians of all decays for which the next-to-leading-order corrections are known. Subsequently, we present the phenomenological implications of these calculations. The values of various parameters are updated, in particular the mass of the newly discovered top quark. One of the central issues in this review are the theoretical uncertainties related to renormalization-scale ambiguities, which are substantially reduced by including next-to-leading-order corrections. The impact of this theoretical improvement on the determination of the Cabibbo-Kobayashi-Maskawa matrix is then illustrated. [S0034-6861(96)00304-2]

Weak decays beyond leading logarithms

The exact form of the form-factor associated with a meson-photon-photon vertex is not known. Different suggestions exist, based on constraints from QCD and on recent experiments. Four different form-factors are studied in this article. 
We calculate decay rates for the decays $\pi^{0}\to \gamma\gamma$, $\eta\to \gamma e^{+}e^{-}$, $\eta\to \mu^{+}\mu^{-} e^{+}e^{-}$} and $\eta\to e^{+}e^{-} e^{+}e^{-}$ and cross sections for the processes $e^{+}e^{-}\to PS e^{+}e^{-}$, where $PS=\pi^{0}$, $\eta$ or $\eta'$. The results depend on the choice of form-factor and we examine if the differences are large enough to distinguish in upcoming experiments. 
The dominant part of the light-by-light contribution to the muon anomalous magnetic moment is also calculated. Here the uncertainty around the choice of form-factor implies that it is possible to estimate a smallest error in the theoretical value of this contribution.

Effects of different Form-factors in Meson-Photon-Photon Transitions and the Muon Anomalous Magnetic Moment

This talk discusses our old work on the hadronic light-by-light contribution to the muon anomalous magnetic moment and some more recent contributions. I discuss the various contributions starting with pseudo-scalar meson exchange, the quark- and pion-loop, as well as scalar and $a_1$-exchange. For the $\pi^0$-exchange I point out a possible large enhancement when only connected contributions are included. For the quark-loop I include some comments about the more recent estimates of this contribution. The pion-loop is discussed in more detail, in particular I discuss our unpublished work on including effects from $a_1$ and the polarizability.

/pdf/hadronic-light-by-light-contribution-to-a-mu-extended-nambu-2i4wp472zu.pdf

Hadronic light-by-light contribution to $a_\mu$: extended Nambu-Jona-Lasinio, chiral quark models and chiral Lagrangians

We discuss various models and Chiral Perturbation Theory results for the $K_{l4}$ form factors $F$ and $G$. We check in how much a simple parametrization with a few parameters can be used to extract information from experiment.

A Parametrization for $K^+\to \pi^+\pi^- e^+\nu$

This talks contains a short introduction to Chiral Perturbation Theory and the existing calculations to two-loop order in the mesonic sector. I include a discussion on which quantities the expansion can be organized in. The present best values of the Low-Energy-Constants as determined from continuum physics are given as well as the assumptions underlying the fits to experimental data. I present plots of masses, decay constants and $f_+(0)$ in $K_{\ell3}$ as a function of quark or meson masses. The talk ends with a list of things for which it would be extremely useful to have good results from lattice QCD calculations.

Quark Mass dependence at Two Loops for Meson Properties

We give a short overview of the theory of the muon anomalous magnetic moment with emphasis on the hadronic light-by-light and the pion loop contribution. We explain the difference between the hidden local symmetry and full VMD pion loop and discuss leading logarithms in the anomalous sector of 2-flavour chiral perturbation theory.

/pdf/the-hadronic-light-by-light-contribution-to-the-muon-2idpha7kjf.pdf

Johan Bijnens

Papers

Effects of different Form-factors in Meson-Photon-Photon Transitions and the Muon Anomalous Magnetic Moment

Hadronic light-by-light contribution to $a_\mu$: extended Nambu-Jona-Lasinio, chiral quark models and chiral Lagrangians

A Parametrization for $K^+\to \pi^+\pi^- e^+\nu$

Quark Mass dependence at Two Loops for Meson Properties

The hadronic light-by-light contribution to the muon anomalous magnetic moment and renormalization group for EFT