Sound shell model for acoustic gravitational wave production at a first-order phase transition in the early Universe

Understand

A model for the acoustic production of gravitational waves at a first order phase transition is presented.

• The source of gravitational radiation is the sound waves generated by the explosive growth of bubbles of the stable phase.
• The model assumes that the sound waves are linear and that their power spectrum is determined by the characteristic form of the sound shell around the expanding bubble.
• The predicted power spectrum has two length scales, the average bubble separation and the sound shell width when the bubbles collide.