Mark Hindmarsh, Stephan J. Huber, Kari Rummukainen, David J. Weir
We report on the first 3-dimensional numerical simulations of first-order phase transitions in the early universe to include the cosmic fluid as well as the scalar field order parameter. We calculate the gravitational wave (GW) spectrum resulting from the nucleation, expansion and collision of bubbles of the low-temperature phase, paying particular attention to those sourced by the fluid. We find that the fluid continues to be a source of GWs long after the bubbles have merged, a new effect not taken into account in previous modelling of the GW source based on the envelope approximation. The kinetic energy of the fluid is in the form of compression waves: the main source of the GWs after a phase transition is therefore the sound the bubbles make.
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http://arxiv.org/abs/1304.2433
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