Traces of Extra Dimensions in Cosmology

Abstract

In this thesis, we discuss the observational consequences of extra dimensions on cosmological phenomena. We begin with an overview of extra dimensions, from the
initial ideas of Kaluza and Klein to the more recent concept of braneworld models and
in particular review the cosmological aspects of the DGP braneworld model, which can
produce late time acceleration. We then go on to consider the asymmetric brane model,
comparing its cosmology to the standard concordance and DGP models and showing
how the asymmetric model can be considered a one-parameter extension of the DGP
model over a range of relevant physical scales. Using type Ia supernovae data and the
cosmic microwave background shift parameter, the effect of this new parameter on the
expansion history of the universe is considered. We then turn our attention to cosmic
string loops, which emit bursts of gravitational radiation, produced by cusps and kinks
on the loops. We investigate the kinematic effect extra dimensions will have on these
gravitational wave bursts and find that the effects of the additional dimensions are more
pronounced for cusps than for kinks: cusps are rounded off and their probability of
formation is reduced, however, the probability of kink formation is unchanged. Finally,
we recompute the gravitational wave bursts taking the various factors into account and
look at the implications of this recalculation for the LIGO and LISA gravitational wave
detectors, find that both signals, and in particular the cusp signal, have a potentially
significant damping, and consider the implications for the detection of extra dimensions.