Compiled to illustrate the recent history of Quantum Field Theory and its trends, this collection of selected reprints by Jurg Froehlich, a leading theoretician in the field, is a comprehensive guide of the more mathematical aspects of the subject. Results and methods of the past fifteen years are reviewed. The analytical methods employed are non-perturbative and, for the larger part, mathematically rigorous. Most articles are review articles surveying certain important developments in quantum field theory and guiding the reader towards the original literature.The volume begins with a comprehensive introduction by Jurg Froehlich.The theory of phase transitions and continuous symmetry breaking is reviewed in the first section. The second section discusses the non-perturbative quantization of topological solitons. The third section is devoted to the study of gauge fields. A paper on the triviality of 4 - theory in four and more dimensions is found in the fourth section, while the fifth contains two articles on "random geometry". The sixth and final part addresses topics in low-dimensional quantum field theory, including braid statistics, two-dimensional conformal field theory and an application to condensed matter theory.

Compiled to illustrate the recent history of quantum field theory and its trends, this collection of selected reprints by Frohlich aims to be a comprehensive guide of the more mathematical aspects of the subject. Results and methods of the past 15 years are reviewed. The analytical methods employed are non-perturbative and, for the larger part, mathematically rigorous. Most articles are review articles surveying certain important developments in quantum field theory and guiding the reader towards the original literature. The theory of phase transitions and spontaneous symmetry breaking is reviewed in the first section. The second section discusses the non-perturbative quantization of topological solitons. The third section is devoted to the study of gauge fields. A paper on the triviality of (labda phi) to the power of 4 - theory in four and more dimensions is found in the fourth section, while the fifth contains two articles on "random geometry". The sixth and final part addresses topics in low-dimensional quantum field theory, including braid statistics, two-dimensional conformal field theory and an application to condensed matter theory. The volume begins with a comprehensive introduction by Jurg Frohlich.

This book reviews recent results on low-dimensional quantum field theories and their connection with quantum group theory and the theory of braided, balanced tensor categories. It presents detailed, mathematically precise introductions to these subjects and then continues with new results. Among the main results are a detailed analysis of the representation theory of U (sl ), for q a primitive root of unity, and a semi-simple quotient thereof, a classfication of braided tensor categories generated by an object of q-dimension less than two, and an application of these results to the theory of sectors in algebraic quantum field theory. This clarifies the notion of "quantized symmetries" in quantum fieldtheory. The reader is expected to be familiar with basic notions and resultsin algebra. The book is intended for research mathematicians, mathematical physicists and graduate students.

This book collects lecture courses and seminars given at the Les Houches Summer School 2010 on "Quantum Theory: From Small to Large Scales." Fundamental quantum phenomena appear on all scales, from microscopic to macroscopic. Some of the pertinent questions include the onset of decoherence, the dynamics of collective modes, the influence of external randomness and the emergence of dissipative behaviour. Our understanding of such phenomena has been advanced by the study of model systems and by the derivation and analysis of effective dynamics for large systems and over long times. In this field, research in mathematical physics has regularly contributed results that were recognized as essential in the physics community. During the last few years, the key questions have been sharpened and progress on answering them has been particularly strong. This book reviews the state-of-the-art developments in this field and provides the necessary background for future studies. All chapters are written from a pedagogical perspective, making the book accessible to master and PhD students and researchers willing to enter this field.

English summary: The mechanical-deterministic world-view plunged into crisis at the end of the 19th century and for the next 85 years quantum mechanics succeeded the naive realism of the old world view. Jorg Frohlich considers this paradigm shift and reflects on the physics of the 20th century from a historical-philosophic perspective: What stood behind these concepts, who essentially contributed to the new forms of knowledge? After considering these questions, he comes to the conclusion: theoretical physics does not explain natural events, it only describes them. German description: Das mechanistisch-deterministische Weltbild geriet am Ende des 19. Jahrhunderts in eine Krise - und vor nunmehr 85 Jahren folgte der Abschied vom naiven Realismus des alten Weltbildes mit der Quantenmechanik. Juerg Frohlich nimmt diese Paradigmenwechsel auf und reflektiert die Physik des 20. Jahrhunderts aus historisch-philosophischer Perspektive: was steht hinter diesen Begriffen, wer trug wesentlich zu neuen Erkenntnissen bei? Nach Erorterung dieser Fragen kommt er zu dem Schluss: aDie theoretische Physik erklart das Naturgeschehen nicht, sie beschreibt es nur.