Gravitational wave spectra from strongly supercooled phase transitions

Understand

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.