Topological defects: fossils of an anisotropic era?

Abstract

We consider the evolution of domain walls produced during an anisotropic phase in the very early universe, showing that the resulting network can be very anisotropic. If the domain walls are produced during an inflationary era, the network will soon freeze out in comoving coordinates retaining the imprints of the anisotropic regime, even though inflation makes the universe isotropic. Only at late times, when the typical size of the major axis of the domain walls becomes smaller than the Hubble radius, does the network evolve rapidly towards isotropy. Hence, we may hope to see imprints of the anisotropic era if by today the typical size of the major axis of the domain walls is of the order of the Hubble radius, or if the walls re-entered it only very recently. Depending on the mass scale of the domain walls, there is also the possibility that they re-enter at earlier times, but their evolution remains friction-dominated until recently, in which case the signatures of the anisotropic era will be much better preserved. These effects are expected to occur in generic topological defect models.