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| Book/Dissertation / PhD Thesis | PUBDB-2021-04477 |
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2021
Verlag Deutsches Elektronen-Synchrotron DESY
Hamburg
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Please use a persistent id in citations: doi:10.3204/PUBDB-2021-04477
Report No.: DESY-THESIS-2021-020
Abstract: In the light of upcoming gravitational wave experiments like the Laser Interferometer SpaceAntenna (LISA) we aim to improve the understanding of early universe first-order phasetransitions.In this thesis, the central subject of study is the energy budget of phase transitions. Thisthermodynamic quantity can be studied microscopically in equilibrium finite temperaturequantum field theory. Understanding the energy budget is essential as it enters the normal-ization of the gravitational wave (GW) spectrum generated from first-order phase transitions.We provide a new method for precise determination of the energy budget, which is for onceeasy to implement and also model-independent up to the temperature dependence in thespeed of sound (of the early universe plasma). Following from the new method, the resultingstochastic gravitational wave signal is not only parametrized by the phenomenological GWparameters α, β, Tn, vw but now also the speed of sound in the symmetric and broken phase inthe plasma, which possibly introduces previously unconsidered degeneracy in the GW spec-trum.We validate and study the new method by applying it to several semi-realistic and realisticequations of state. As LISA is complementary to the Large Hadron Collider (LHC) as aprobe of the electroweak scale, we set our focus here. In particular, we study the real scalarextended Standard Model, which can lead to a first-order electroweak phase transition. Weshow that corrections to the speed of sound in this minimal extension are small yet not gener-ically negligible and show further under what conditions we expect large deviations.We then go more into model-building details and investigate the vacuum properties of therealization of a first-order electroweak phase transition with a singlet and varying effectiveYukawa couplings. For a specific UV completion based on Froggatt-Nielsen fields, we explic-itly show that naively expected instabilities cannot arise in the effective field theory picture,which is the crucial regime for the electroweak phase transition and possibly also for baryo-genesis.To complete the discussion, we connect to the experimental prospects of LISA for detecting astochastic GW background from a first-order phase transition. Here we are working towardsdissolving degeneracy in those mentioned above phenomenological GW parameters. As astart, we focus on the question under what conditions spectral information can be extractedin the form of a double-broken power law. Such feature is theoretically expected and relatedto the bubble wall velocity vw. Actual LISA data is currently unavailable. We thus generateLISA mock data and apply data reconstruction techniques relying on likelihood fits.
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