Preview

PDF, English - main document Download (3MB) | Lizenz: Impact of Gravitational Waves from First-Order Phase Transitions on Structure Formation by Döring, Christian underlies the terms of Creative Commons Attribution 4.0

Abstract

In this thesis we investigate the possibility that gravitational waves emitted from a first-order phase transition exhibit enough power to alter or generate fluctuations in the primordial plasma of the early universe and in turn imprint new features into the matter power spectrum. We approach this task by performing a second order perturbative expansion of two coupled non-linear equations that monitor the evolution of energy density gradients in the 1+3 covariant formulation of cosmology. As a result, we find that adiabatic density fluctuations at second order can be generated from inhomogeneities in the gravitational wave energy density on sub-horizon scales. We interpret these fluctuations as baryon acoustic oscillations seeded by gravity radiation and derive their transferfunction to study their impact on the matter power spectrum. Strength and scale of the imprinted signatures depend on three phase transition parameters, namely the latent heat, the duration and the time at which gravitational waves are released. The amplitude of the signatures is limited by the cosmic variance bound on the matter power spectrum. We use this constraint to deduce limits for these three parameters and translate them into a new exclusion region for the relic stochastic gravitational wave background today. Finally, we discuss our results in the context of first-order phase transitions occurring in particle models.