Simple random walks - or equivalently, sums of independent random vari ables - have long been a standard topic of probability theory and mathemat ical physics. In the 1950s, non-Markovian random-walk models, such as the self-avoiding walk,were introduced into theoretical polymer physics, and gradu ally came to serve as a paradigm for the general theory of critical phenomena. In the past decade, random-walk expansions have evolved into an important tool for the rigorous analysis of critical phenomena in classical spin systems and of the continuum limit in quantum field theory. Among the results obtained by random-walk methods are the proof of triviality of the cp4 quantum field theo ryin space-time dimension d (::::) 4, and the proof of mean-field critical behavior for cp4 and Ising models in space dimension d (::::) 4. The principal goal of the present monograph is to present a detailed review of these developments. It is supplemented by a brief excursion to the theory of random surfaces and various applications thereof. This book has grown out of research carried out by the authors mainly from 1982 until the middle of 1985. Our original intention was to write a research paper. However, the writing of such a paper turned out to be a very slow process, partly because of our geographical separation, partly because each of us was involved in other projects that may have appeared more urgent.

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.

A collection of 22 reprints of Frohlich's articles on non-perturbative aspects of quantum field theory, more than half of them of a review character, on topics in phase transitions and continuous symmetry breaking; non-perturbative quantization of topological solitons; gauge theories, including (the infrared problem in) quantum electrodynamics; random geometry (quantum gravity and strings); and low-dimensional QFT--two-dimensional conformal field theory, three-dimensional (gauge) theories. No index. Paper edition (unseen), $48. Annotation copyrighted by Book News, Inc., Portland, OR

This book contains selected papers of Jürg Fröhlich, one of the most outstanding mathematical physicists of our time, on the subject of statistical mechanics. In an extensive introduction, Jürg Fröhlich sets his results into a wider context and gives precious information on the genesis of his work from both a historical and a methodological perspective. It is not only an overview of current and future research directions in statistical mechanics, but also relates this subject with other branches of contemporary physics and mathematics. All papers in this collection bear Jürg Fröhlich’s signature in terms of a delicate balance between mathematical rigor and physical significance. They cover thirty years of his work on statistical physics, ranging from the most basic foundational questions in atomism and thermodynamics via the description of phase transitions and critical phenomena up to disordered systems and the study of many-body systems in condensed matter physics, including the quantum Hall effect. The wide range of topics covered in this compendium reflects the breadth of Jürg Fröhlich’s interests, and the last chapters reveal an outlook towards some of his more recent research areas.

Low-dimensional statistical models are instrumental in improving our understanding of emerging fields, such as quantum computing and cryptography, complex systems, and quantum fluids. This book of lectures by international leaders in the field sets these issues into a larger and more coherent theoretical perspective than is currently available.