Sum Rules and Bose-Einstein Condensation
arXiv:cond-mat/9311024
Abstract
Various sum rules accounting for the coupling between density and particle excitations and emphasizing in an explicit way the role of the Bose-Einstein condensation are discussed. Important consequences on the fluctuations of the particle operator as well as on the structure of elementary excitations are reviewed. These include a recent generalization of the Hohenberg-Mermin-Wagner theorem holding at zero temperature. (To appear in "Bose-Einstein Condensation", A.Griffin, D.Snoke and S.Stringari eds., Cambridge Univ. Press)
16 pages, Plain TeX, no figures, UTF-308-10/93