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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 uctuations 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.