Physics
Scientific paper
Aug 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phdt........21s&link_type=abstract
Proquest Dissertations And Theses 2007. Section 0330, Part 0606 195 pages; [Ph.D. dissertation].United States -- Illinois: The
Physics
Modified Gravity, Dark Energy, Dvali-Gabadadze-Porrati Gravity, General Relativity
Scientific paper
We study the effects of introducing modifications to general relativity ("GR") at large scales as an alternative to exotic forms of matter required to replicate the observed cosmic acceleration. We survey the effects on cosmology and solar-system tests of Dvali-Gabadadze-Porrati ("DGP") gravity, f ( R ) he changes to the background expansion history of the universe, these modifications have substantial impact on structure formation and its observable predictions.
For DGP, we develop a scaling approximation for the behaviour of perturbations off the brane, for which the predicted integrated Sachs-Wolf ("ISW") effect is much stronger than observed, requiring new physics at around horizon scale to bring it into agreement with data. We develop a test based on cross-correlating galaxies and the ISW effect which is independent of the initial power spectrum for perturbations and is a smoking-gun test for DGP gravity.
For f ( R ) models, we find that, for the expansion history to resemble that of Lambda-CDM, it is required that the second derivative of f with respect to R be non-negative. We then find the conditions on f ( R ) which allow this subset of models to pass solar-system tests. Provided that gravity behave like GR in the galaxy, these constraints are weak. However, for a model to allow large deviations from GR in the cosmology, the galactic halo must differ significantly from that predicted by structure evolution in GR. We then discuss the effect that these models have on structure formation, and find that even in the most conservative of models, percent-level deviations in the matter power spectrum will exist and should be detectable in the future.
Finally, for MSG, we investigate the cosmology of a theory of gravity with a modified constraint structure. The acceleration era can be replicated in these models; however, linear perturbations become unstable as the universe begins to accelerate. Once the perturbations become non-linear, the model reverts to GR, regaining stability. This leaves a significant imprint on structure-formation probes, but one which we cannot calculate in the linear approximation.
No associations
LandOfFree
Modified gravity as dark energy does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Modified gravity as dark energy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modified gravity as dark energy will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1799635