Onset of cosmological turbulence

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http://urn.fi/URN:NBN:fi-fe201804208600
Title: Onset of cosmological turbulence
Author: Dahl, Jani
Contributor: University of Helsinki, Faculty of Science, Department of Physics
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
URI: http://urn.fi/URN:NBN:fi-fe201804208600
http://hdl.handle.net/10138/273484
Thesis level: master's thesis
Discipline: Theoretical Physics
Teoreettinen fysiikka
Teoretisk fysik
Abstract: At the end of the inflationary epoch, about 10^(−12) seconds after the Big Bang singularity, the universe was filled with plasma consisting of quarks and gluons. At some stage the cooling of the universe could have led to the occurrence of first-order cosmological phase transitions that proceed by nucleation and expansion of bubbles all over the primordial plasma. Cosmological turbulence is generated as a consequence of bubble collisions and acts as a source of primordial gravitational waves. The purpose of this thesis is to provide an overview of cosmological turbulence as well as the corresponding gravitational wave production, and compile some of the results obtained to this day. We also touch on the onset of cosmological turbulence by analysing shock formation. In the one-dimensional case considering only right-moving waves, the result is Burgers’ equation. The development of a power spectrum with random initial conditions under Burgers’ equation is calculated numerically using the Euler method with sufficiently low step sizes. Both in the viscid and inviscid cases, the result is the presence of a −8/3 power law in the inertial range at the time of shock formation.


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