Gravitational waves from bubble dynamics: Beyond the Envelope

Ryusuke Jinno, Masahiro Takimoto

Published 2017-07-11Version 1

We study gravitational-wave production from bubble dynamics (bubble collisions and sound waves) during a cosmic first-order phase transition with an analytic approach. We model the system with the thin-wall approximation but without the envelope approximation often adopted in the literature. We first write down analytic expressions for the gravitational-wave spectrum, and then evaluate them with numerical methods. It is found that, in the long-lasting limit of the collided walls, the spectrum grows from $\propto f^3$ to $\propto f^1$ for low frequencies, showing a significant enhancement compared to the one with the envelope approximation. It is also found that the spectrum saturates in the same limit, indicating a decrease in the correlation of the energy-momentum tensor at late times. The bubble walls in our setup are considered as modeling the scalar field configuration and/or the bulk motion of the fluid, and therefore our results have implications to gravitational-wave production from both bubble collisions (scalar dynamics) and sound waves (fluid dynamics).