On Self-Similar Global Textures in an expanding Universe

Abstract

We discuss self-similar solutions to $O(4)$ textures in Minkowski space and in flat Friedmann-Robertson-Walker backgrounds. We show that in the Minkowski case there exist no solutions with winding number greater than unity. However, we find besides the known solution with unit winding number also previously unknown solutions corresponding to winding number less than one. The validity of the non-linear sigma model approximation is discussed. We point out that no spherically symmetric exactly self-similar solutions exist for radiation or matter dominated FRW cosmologies, but we find a way to relax the assumptions of self-similarity that give us approximative solutions valid on intermediate scales.