Preface

This volume contains the written versions of most of the invited lectures presented at the "44. Internationale Universitatswochen fur Theoretische Physik" in Schladming, Austria, which took place from March 11th to 18th, 2006. The title of the school was "Hadron Structure and Nonperturbative QCD". We considered this to be a timely topic for mainly two reasons: Firstly, the plans for future experimental facilities dedicated to hadron physics, such as the FAIR pro ject at GSI, Darmstadt, and the 12 GeV upgrade at Jefferson Laboratory promise exciting discoveries and broad insight on the experimental side. Secondly, substantial theoretical progress has been made in nonperturbative Quantum Chromodynamics (QCD) in recent years. The lectures given during this school confirmed these expectations. We are especially happy to have received encouraging and positive comments by the participating students. This makes us confident that the school has been and these lecture notes are contributions to the excitement of both young researchers and established scientists in this promising area of research.

Among the most intriguing phenomena in hadron physics is confinement: quarks and gluons, while being the elementary fields of QCD, have never been observed as free particles. A rigorous proof of confinement, based on QCD, is considered to be of outstanding importance for our understanding of nature. Its significance can also be inferred from the fact that the Clay Mathematics Institute of Cambridge ranks this as one of the seven Millennium Problems by offering a prize of one million dollars for such a proof.

Even without a proof, QCD provides some evidence why quarks and gluons are confined. Jeff Greensite (San Francisco State University) discussed several scenarios of quark confinement in great detail. His lectures introduced the mathematical apparatus needed for a thorough understanding of non-abelian Yang-Mills theory as well as the advantages and drawbacks of various confinement scenarios such as the center vortex picture.

Craig D. Roberts (Argonne National Laboratory) presented a consistent description of hadrons in terms of their underlying substructure. He explained why spontaneous chiral symmetry breaking and dynamical mass generation play a central role in hadron physics and discussed the tools necessary to study these phenomena in continuum quantum field theory focusing on implications for our understanding of meson and baryon properties.

Anthony W. Thomas (Jefferson Lab) provided an outline of the 12 GeV upgrade at Jefferson Lab and the science explored there. Furthermore he presented results on nucleon properties as extracted from the results of lattice Monte-Carlo calculations.

Thorsten Feldmann (University of Siegen) gave an introduction to the concept of generalized parton distributions (GPDs) starting from the well-known structure functions. He explained the phenomenology as well as the interpretation of GPDs thereby providing deep insight into the complex structure of nucleons.

James M. Zanotti (University of Edinburgh) started his lectures with an introduction to lattice QCD and moved on to the corresponding description of the nucleon and its form factors. He managed to present state-of-the-art results for the moments of the nucleon structure function in a way that allowed the audience to critically access the progress made in the last few years.

His presentation of the results for GPDs provided an outstanding concluding lecture of this school.

In addition, we had excellent lectures by Marco Stratmann (University of Regensburg) on the physics of the nucleon spin and Thomas R. Hemmert (Technical University Munich) on effective field theories.

As organizers we cordially thank the lecturers on behalf of all participants. We are confident that their efforts to present recent research have been beneficial to all who attended this school, independent of whether they are young students at the beginning of their career or established scientists; in the same way these lecture notes should be equally beneficial to a broad audience.

We are very grateful to the sponsors of the school, hereby first of all the Austrian Ministry of Education, Sciences and Arts. We acknowledge generous support by the Government of Styria, the University of Graz, and the City of Schladming. We received further support from the companies RICOH and Computer Majer.

Reinhard Alkofer, Andreas Krassnigg and Wolfgang Schweiger