Gravitational wave spectra from strongly supercooled phase transitions

Abstract

We study gravitational wave (GW) production in strongly supercooled cosmological phase transitions, taking particular care of models featuring a complex scalar field with a U$(1)$ symmetric potential. We perform lattice simulations of two-bubble collisions to properly model the scalar field gradients, and compute the GW spectrum sourced by them using the thin-wall approximation in many-bubble simulations. We find that in the U$(1)$ symmetric case the low-frequency spectrum is $\propto \omega$ whereas for a real scalar field it is $\propto {\omega }^3$. In both cases the spectrum decays as ${\omega }^{-2}$ at high frequencies.

Comments: 7 pages, 4 figures. published version