Precise gravitational-wave spectrum from tachyonic particle production

Determine the precise gravitational-wave spectrum generated by tachyonic particle production during strongly supercooled cosmological phase transitions, including its amplitude and frequency dependence.

Background

The paper shows that an appreciable fraction of the vacuum energy released during a strongly supercooled phase transition can be transferred into scalar fluctuations through tachyonic particle production. This may generate an additional gravitational-wave signal analogous to that produced by resonant preheating, while the dominant momentum of the produced modes shifts to higher values as the bubble evolves.

Although the authors estimate that the signal could have a sizeable amplitude and a frequency much higher than that of the bubble-collision signal, they do not calculate its final spectrum. A precise prediction requires determining how the time-dependent momentum production and transferred energy shape the gravitational-wave spectrum.