Perfect fluids and symmetry mappings leading to conservation laws

Abstract

Some of the results recently obtained by Glass relating to shear-free perfect fluids are extended and further interpreted. In particular, it is pointed out that certain symmetry methods are fundamental to this type of investigation. This approach of using symmetry mappings (e.g., characterizing vanishing shear) at the level of the matter tensor is seen to naturally lead to considerations of an important family of symmetry properties which include Ricci collineations as a special case. These considerations are used to obtain new conservation expressions holding for perfect fluids.