Excerpt from Dispersion Relations and the Abstract Approach to Field TheoryFurthermore it is assumed that it is possible to define a vacuum state: that is the energy operator should possess a smallest eigenvalue which we normalize to zero. The knowledge of commutation relations for field Operators is almost not necessary. Equation 1) is sufficient.Now we want to examine the vacuum expectation values of quadratic field magnitudes. As the orthogonal system in Hilbert space we shall use in this case, the eigenvectors of the PM operators, which should form a complete set.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.