Homothetic perfect fluid spacetimes

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