Researchers have investigated the production of stochastic gravitational waves associated with the phase transition that marked the end of thermal inflation, a hypothetical phase in the early universe. This study focuses on characterizing the nature of this first-order phase transition and predicting the resulting gravitational wave spectrum, which could be detectable by future observatories.

The phase transition was analyzed using semi-analytic calculations of the bounce action and numerical simulations with the CosmoTransitions tool. Subsequently, its real-time evolution was modeled using a three-dimensional Langevin lattice simulation, which incorporated Hubble expansion and temperature evolution during the process. The lattice simulation results confirmed that the transition proceeds via localized bubble nucleation and growth, rather than a phase-mixing instability, consistent with bounce-action estimates.

Using the parameters derived from these simulations, the gravitational wave spectra generated by bubble collisions and acoustic motions in the plasma were estimated. The results suggest that the predicted stochastic background of gravitational waves lies within the projected sensitivity ranges of future observatories, such as BBO (Big Bang Observer) and DECIGO (Deci-hertz Interferometer Gravitational-wave Observatory). This opens a potential avenue for the experimental detection of phenomena from the primordial universe.

The possibility of detecting these gravitational waves would offer a unique window into the high-energy physics operating in the universe's initial moments, providing direct evidence for cosmological models like thermal inflation and its associated phase transitions. Confirmation of these predictions would allow discrimination between different early universe scenarios and refine our understanding of cosmological evolution.