Numerical simulations of acoustically generated gravitational waves at a first order phase transition

Hindmarsh, Mark, Huber, Stephan J, Rummukainen, Kari and Weir, David J (2015) Numerical simulations of acoustically generated gravitational waves at a first order phase transition. Physical Review D, 92 (12). p. 123009. ISSN 2470-0010

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We present details of numerical simulations of the gravitational radiation produced by a first order thermal phase transition in the early Universe. We confirm that the dominant source of gravitational waves is sound waves generated by the expanding bubbles of the low-temperature phase. We demonstrate that the sound waves have a power spectrum with a power-law form between the scales set by the average bubble separation (which sets the length scale of the fluid flow Lf) and the bubble wall width. The sound waves generate gravitational waves whose power spectrum also has a power-law form, at a rate proportional to Lf and the square of the fluid kinetic energy density. We identify a dimensionless parameter ˜ ΩGW characterizing the efficiency of this “acoustic” gravitational wave production whose value is 8π ˜ ΩGW≃0.8±0.1 across all our simulations. We compare the acoustic gravitational waves with the standard prediction from the envelope approximation. Not only is the power spectrum steeper (apart from an initial transient) but the gravitational wave energy density is generically larger by the ratio of the Hubble time to the phase transition duration, which can be 2 orders of magnitude or more in a typical first order electroweak phase transition.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Theoretical Particle Physics Research Group
Subjects: Q Science > QC Physics
Depositing User: Richard Chambers
Date Deposited: 17 Jan 2017 14:31
Last Modified: 06 Mar 2017 08:19

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Project NameSussex Project NumberFunderFunder Ref
Particle Physics Theory at Royal Holloway and SussexG0742STFC-SCIENCE AND TECHNOLOGY FACILITIES COUNCILST/J000477/1