Shape of the acoustic gravitational wave power spectrum from a first order phase transition

By M. Hindmarsh, S. Huber, K. Rummukainen, D. Weir. 2017

392 citations recorded by the source corpus.

We present results from large-scale numerical simulations of a first order thermal phase transition in the early Universe, in order to explore the shape of the acoustic gravitational wave and the velocity power spectra. We compare the results with the predictions of the recently proposed sound shell model. For the gravitational wave power spectrum, we find that the predicted k−3 behavior, where k is the wave number, emerges clearly for detonations. The power spectra from deflagrations show similar features, but exhibit a steeper high-k decay and an extra feature not accounted for in the model. There are two independent length scales: the mean bubble separation and the thickness of the sound shell around the expanding bubble of the low temperature phase. It is the sound shell thickness which sets the position of the peak of the power spectrum. The low wave number behavior of the velocity power spectrum is consistent with a causal k3, except for the thinnest sound shell, where it is steeper. We present parameters for a simple broken power law fit to the gravitational wave power spectrum for wall speeds well away from the speed of sound where this form can be usefully applied. We examine the prospects for the detection, showing that a LISA-like mission has the sensitivity to detect a gravitational wave signal from sound waves with an RMS fluid velocity of about 0.05c, produced from bubbles with a mean separation of about 10−2 of the Hubble radius. The shape of the gravitational wave power spectrum depends on the bubble wall speed, and it may be possible to estimate the wall speed, and constrain other phase transition parameters, with an accurate measurement of a stochastic gravitational wave background.

View Paper: https://www.semanticscholar.org/paper/6beb3cfc06ff61ac3074253160461b6efb43c9c8

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Citations in the corpus

Towards an all-orders calculation of the electroweak bubble wall velocity (2020, background): “For instance, bubble collisions stir up the charged constituents of the plasma [78], and the associated magnetohydrodynamic turbulence leads to a magnetic field with coherence on the scale of the bubble radius.”
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