Speaker
Description
Gravitational waves from cosmological first-order phase transitions provide a powerful probe of early-Universe physics. While existing semi-analytical models generally predict that cosmic expansion modestly suppresses the resulting gravitational-wave signal, we demonstrate that this expectation is qualitatively reversed for slow transitions. Using the first three-dimensional hydrodynamical simulations in an expanding background to consistently evolve the effective transition strength throughout nucleation, we show that cosmic expansion modifies the mean bubble separation and drives highly nonlinear growth in the gravitational-wave energy content. Consequently, the resulting gravitational wave spectra are amplified by factors of 10 – 100 relative to otherwise identical simulations without expansion. These findings establish cosmic expansion not merely as a required theoretical refinement, but as a crucial physical mechanism that fundamentally alters current signal forecasts and expands the discovery space for future gravitational-wave missions.