
TL;DR
This thesis explores modifications to general relativity, including massive and bimetric gravity theories and Lorentz violation during inflation, to address the universe's accelerated expansion and test gravity on cosmological scales.
Contribution
It introduces new methods for analyzing cosmological perturbations in massive and bimetric gravity and investigates Lorentz violation effects during inflation, providing novel theoretical insights.
Findings
Stable bimetric models can be tested against structure formation data
Certain vector-scalar couplings during inflation are severely constrained by instabilities
Massive gravity theories offer a potential explanation for late-time cosmic acceleration
Abstract
The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates the other forces mostly on large scales, cosmological probes provide an ideal testing ground for theories of gravity. In this thesis, we describe two complementary approaches to the problem of testing gravity using cosmology. In the first part, we discuss the cosmological solutions of massive gravity and its generalisation to a bimetric theory. These theories describe a graviton with a small mass, and can potentially explain the late-time acceleration in a technically-natural way. We describe these self-accelerating solutions and investigate the cosmological perturbations in depth, beginning with an investigation of their linear…
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Taxonomy
TopicsCosmology and Gravitation Theories
