Cosmology beyond Einstein / Adam Ross Solomon.

Supervisor's Foreword; Abstract ; Parts of this thesis have been published in the following journal articles:; References; Acknowledgements; Contents; 1 Introduction; 1.1 Conventions; 1.2 General Relativity; 1.3 The Cosmological Standard Model; 1.4 Linear Perturbations Around FLRW; 1.5 Inflation; References; 2 Gravity Beyond General Relativity; 2.1 Massive Gravity and Bigravity; 2.1.1 Building the Massive Graviton; 2.1.2 Ghost-Free Massive Gravity; 2.1.3 Cosmological Solutions in Massive Bigravity; 2.2 Einstein-Aether Theory; 2.2.1 Pure Aether Theory; 2.2.2 Coupling to a Scalar Inflation

2.2.3 Einstein-Aether CosmologyReferences; Part I A Massive Graviton; 3 Cosmological Stability of Massive Bigravity; 3.1 Linear Cosmological Perturbations; 3.1.1 Linearised Field Equations; 3.1.2 Counting the Degrees of Freedom; 3.1.3 Gauge Choice and Reducing the Einstein Equations; 3.2 Stability Analysis; 3.3 Summary of Results; References; 4 Linear Structure Growth in Massive Bigravity; 4.1 Perturbations in the Subhorizon Limit; 4.2 Structure Growth and Cosmological Observables; 4.2.1 Modified Gravity Parameters; 4.2.2 Numerical Solutions; 4.3 Summary of Results; References

5 The Geometry of Doubly-Coupled Bigravity5.1 The Lack of a Physical Metric; 5.2 Light Propagation and the Problem of Observables; 5.3 Point Particles and Non-Riemannian Geometry; 5.4 Summary of Results; References; 6 Cosmological Implications of Doubly-Coupled Massive Bigravity; 6.1 Doubly-Coupled Bigravity; 6.2 Cosmological Equations and Their Solutions; 6.2.1 Algebraic Branch of the Bianchi Constraint; 6.2.2 Dynamical Branch of the Bianchi Constraint; 6.3 Comparison to Data: Minimal Models; 6.4 Special Parameter Cases; 6.4.1 Partially-Massless Gravity

6.4.2 Vacuum Energy and the Question of Self-Acceleration6.4.3 Maximally-Symmetric Bigravity; 6.5 Summary of Results; References; 7 Cosmological Implications of Doubly-Coupled Massive Gravity; 7.1 Cosmological Backgrounds; 7.2 Do Dynamical Solutions Exist?; 7.3 Einstein Frame Versus Jordan Frame; 7.4 Massive Cosmologies with a Scalar Field; 7.5 Adding a Perfect Fluid; 7.6 Mixed Matter Couplings; 7.7 Summary of Results; References; Part II Lorentz Violation; 8 Lorentz Violation During Inflation; 8.1 Stability Constraint in Flat Space; 8.2 Cosmological Perturbation Theory

8.2.1 Perturbation Variables8.2.2 Linearised Equations of Motion; 8.3 Spin-1 Cosmological Perturbations; 8.3.1 Slow-Roll Limit; 8.3.2 Full Solution for the Vector Modes; 8.3.3 Tachyonic Instability; 8.3.4 What Values Do We Expect for Lambda?; 8.4 Spin-0 Cosmological Perturbations: Instability and Observability; 8.4.1 The Spin-0 Equations of Motion; 8.4.2 The Instability Returns; 8.4.3 The Small-Coupling Limit; 8.4.4 The Large-Coupling Limit: The Phi Evolution Equation; 8.4.5 The Large-Coupling Limit: CMB Observables; 8.5 Case Study: Quadratic Potential; 8.5.1 Slow-Roll Inflation: An Example