This volume of the Encyclopaedia contains threecontributions in the field of complex analysis. The topicstreated are mean periodicity and convolutionequations, Yang-Mills fields and the Radon-Penrose transform, andstringtheory. The latter two have strong links with quantumfield theory and the theory of general relativity. In fact, the mathematical results described inthe book arose fromthe need of physicists to find a sound mathematical basisfor their theories. The authors present their material inthe formof surveys which provide up-to-date accounts ofcurrent research. The book will be...

In this part, we present a survey of mean-periodicity phenomena which arise in connection with classical questions in complex analysis, partial differential equations, and more generally, convolution equations. A common feature of the problem we shall consider is the fact that their solutions depend on tech niques and ideas from complex analysis. One finds in this way a remarkable and fruitful interplay between mean-periodicity and complex analysis. This is exactly what this part will try to explore. It is probably appropriate to stress the classical flavor of all of our treat ment. Even...