Gravitational waves as string vacua I

Recent results on the role of gravitational waves in string theory are reviwed. Motivations for the research and an organic view of the topic are furnished. Short exposition of the elements of string theory in the Polyakov formalism is provided, with particular emphasis on the evaluation of the Weyl and super-Weyl anomalies. Relevant results on the plane wave solutions of the Einstein equations are listed and a way of solving a quantum field theory in such backgrounds is presented. The results obtained for theS-matrix of the field theory and (singular) expectation values of its energy momentum tensor will be linked to string physics in subsequent parts of this review.This review article is based on the PhD thesis of the author defended in 1989 at SISSA, Trieste. It is divided into three parts with independent abstracts and tables of contents.