Gravitational waves from bubble collisions and fluid motion in strongly supercooled phase transitions

We estimate the gravitational wave spectra generated in strongly supercooled phase transitions by bubble collisions and fluid motion. derive analytically thin-wall approximation efficiency factor that determines share of energy released transition between scalar field fluid. perform numerical simulations including as a function radius separately for all points on surfaces to take into account their different collision times. find does not significantly change show result can be approximated multiplying spectrum obtained without its value at $R_{\rm eff} \simeq 5/\beta$, where $\beta$ is approximate inverse duration transition. also provide updated fits produced from both motion depending behaviour sources after collision.