Decay of three-dimensional acoustic turbulence and the resulting power spectrum for cosmological gravitational waves

by Jani Dahl (University of Helsinki)

Wednesday 12 Jun 2024, 13:30 → 14:30 Europe/Stockholm

Albano 3: 6228 - Mega (22 seats) (Albano Building 3)

Gravitational waves (GW) from a phase transition associated with the generation of the masses of elementary particles are within the reach of future space-based detectors such as LISA. A key determinant of the intensity of the GWs is the lifetime of the acoustic turbulence which follows the transition. We have simulated acoustic turbulence in three dimensions using a highly optimized Python code and study the decay of the shocks and derive simple functional forms for the time evolution of the kinetic energy and the integral length scale at late times using the physical properties of the system. We make a new prediction for the universal shape of the energy spectrum by using its self-similar decay properties and the shape of individual shocks. The obtained model for the spectrum and the decay is used to build an estimate for the GW power spectrum generated by decaying acoustic turbulence under approximations where the expansion of the universe can be neglected. The decay is found to bring about a convergence in the spectral amplitude and the peak power law that leads to a shallower power law than in the stationary case.