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.

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PYTHIA 6.4 Physics and Manual

We present a holographic dual of four-dimensional, large N_c QCD with massless flavors. This model is constructed by placing N_f probe D8-branes into a D4 background, where supersymmetry is completely broken. The chiral symmetry breaking in QCD is manifested as a smooth interpolation of D8 - anti-D8 pairs in the supergravity background. The meson spectrum is examined by analyzing a five-dimensional Yang-Mills theory that originates from the non-Abelian DBI action of the probe D8-brane. It is found that our model yields massless pions, which are identified with Nambu-Goldstone bosons associated with the chiral symmetry breaking. We obtain the low-energy effective action of the pion field and show that it contains the usual kinetic term of the chiral Lagrangian and the Skyrme term. A brane configuration that defines a dynamical baryon is identified with the Skyrmion. We also derive the effective action including the lightest vector meson. Our model is closely related to that in the hidden local symmetry approach, and we obtain a Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin-type relation among the couplings. Furthermore, we investigate the Chern-Simons term on the probe brane and show that it leads to the Wess-Zumino-Witten term. The mass of the \eta' meson is also considered, and we formulate a simple derivation of the \eta' mass term satisfying the Witten-Veneziano formula from supergravity.

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Low energy hadron physics in holographic QCD

https://cds.cern.ch/record/192078/files/198811120.pdf

The Role of Resonances in Chiral Perturbation Theory

http://cds.cern.ch/record/326993/files/9705477.pdf

Quantum chromodynamics and other field theories on the light cone

The hidden-charm pentaquark and tetraquark states

Nonlinear Realization and Hidden Local Symmetries

We suggest that the $\ensuremath{\rho}$ meson is a dynamical gauge boson of a hidden local symmetry in the non-linear chiral Lagrangian. The origin of the $\ensuremath{\rho}$-meson mass is understood as the Higgs mechanism of the hidden local symmetry. The low-energy dynamics of $\ensuremath{\rho}$, $\ensuremath{\pi}$, and matter fields, including the Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin relation and $\ensuremath{\rho}$-coupling universality, is consistently described in this new framework. The electromagnetic interaction can be introduced in a unique manner, which gives a successful explanation of $\ensuremath{\rho}$ dominance of the photon coupling.

Is the ρ Meson a Dynamical Gauge Boson of Hidden Local Symmetry

We propose a scale-invariant hypercolor model with a nontrivial ultraviolet fixed point having large anomalous dimension, which resolves the notorious flavor-changing neutral-current problem in hypercolor models, and at the same time predicts a ${J}^{\mathrm{PC}}={0}^{++}$ Nambu-Goldstone boson (dilaton) associated with the spontaneous breakdown of the scale invariance.

Koichi Yamawaki

Papers

Nonlinear Realization and Hidden Local Symmetries

Is the ρ Meson a Dynamical Gauge Boson of Hidden Local Symmetry

Scale-invariant hypercolor model and a dilaton.

Hidden local symmetry at loop: A New perspective of composite gauge boson and chiral phase transition

Dynamical electroweak symmetry breaking with large anomalous dimension and t quark condensate