Cosmic structure from phase transitions

Abstract

Motivated by recent observations suggesting that structures in the Universe appear to be concentrated on the walls of bubbles that surround giant voids, we examine the possibility that the observed structure may have resulted from a first order phase transition that occured after inflation and which proceeded by quantum tunnelling and the formation of bubbles of true vacuum. Since we lack a fundamental theory of particle physics that would define the scalar field responsible for the second phase change and predict the scale of the resulting structures, we instead examine two similar parametrised forms for the potential motivated by the standard Higgs model, and attempt to determine values of the parameters that can reproduce the kind of structures that are observed through bubble wall collisions. The method deployed is quite general and can be applied to any phase transition that occured after inflation. It is found that although the shape of the required potential and its coupling can be determined, the epoch of the proposed second phase transition is in general not specified by the observed structures. The full verification or otherwise of our proposal will require not only a more detailed consideration of its predictions for the large scale structure of the Universe and its compatibility with the cosmic microwave background radiation but also the embedding of our ideas in a credible theory of particle physics beyond the Standard Model.