HOMOTHETIC PERFECT FLUID SPACETIMES

A brief summary of results on homotheties in general relativity is giv en, including general information about spacetimes admitting an r-para meter group of homothetic transformations for r > 2, as well as some s pecific results on perfect fluids. Attention is then focused on inhomo geneous models, in particular on those with a homothetic group H-4 (ac ting multiply transitively) and H-3. A classification of all possible Lie algebra structures along with (local) coordinate expressions for t he metric and homothetic vectors is then provided (irrespectively of t he matter content) and some new perfect fluid solutions are given and briefly discussed.