by
Mikael von Strauss(Stockholm University, Department of Physics)
→
Europe/Stockholm
A5:1041
A5:1041
Description
In this thesis we present work done in an analysis of models of brane induced gravity.
These are higher dimensional generalizations of Einstein's General relativity where our
universe is considered as a brane in a higher dimensional bulk and where the gravitational
dynamics on the brane is enhanced. This provides a modication of gravity on the brane
as compared to ordinary general relativity, primarily at very large distances. These
models are therefore very interesting for adressing the cosmological constant problem.
Even though the basic setup is natural to consider from the perspective of eective
eld theory and also follow from certain string theoretical considerations, the models
have been plagued by inconsistencies in the form of unstable modes. In particular, a
ghostlike and tachyonic scalar mode appears already at the linear level in a perturbative
treatment. In order to gain a deeper insight into the nature of these consistency problems
we have revisited the models, performing a more extensive analysis of the generic models
than has previously been done. We have worked entirely in a gauge invariant formalism
in order not to be obscured by gauge issues. We have also incorporated an eective
thickness of the brane in our analysis and performed an explicit analysis of the eect of
contributions from the extrinsic geometry. Although our analysis has been carried out
at the linear level in a perturbative treatment we are able to get a deeper understanding
of the unstable mode and illuminate some of the diculties of these models that would
likely persist even in a full nonlinear analysis.