Large-Scale Structure Formation in Bimetric Gravity

Abstract

One of the most prominent questions in modern cosmology is the origin of the accelerated expansion of the universe. A solution might lie in modifying gravity in the infrared by adding a small mass to its mediating particle. In recent years, dRGT massive gravity and its dynamical extension Hassan-Rosen bimetric massive gravity have been shown to be classically consistent theories. This prompts for a phenomenological investigation of their predictions in cases already examined in general relativity, such as in sphericallysymmetric geometries and on cosmological scales. The thesis, conducted within the Cosmology, Particle Astrophysics and String Theory group at Stockholm University, elaborates on aspects related to the evolution of large-scale structures through analysis of the bimetric equations of motion for linear perturbations. We review the foundations of relativistic perturbation theory in general relativity. A particular emphasis is placed on superhorizon signatures with the integrated Sachs-Wolfe effect as a candidate mechanism. Moreover, we present the theoretical framework of bimetric massive gravity with applications to cosmology, both on the background level and concerning linear perturbations. The single-coupled theory with FLRW ansätze for the background metrics is investigated in the self-accelerating minimal bimetric β1− and the infinite-branch β1β4−models, where the latter has attracted significant interest recently, with a normalization density condition provided by the Planck 2013 survey. We solve the system of equations of motion for the linear scalar perturbation fields in the Fg = Ff = 0−gauge following the notation of Solomon et al. and find an additional alternative by examining the Noether identities for the second-order perturbed action based on the method demonstrated by Lagos et al. To conclude, we plot the evolution of the linearized bimetric gravitational potentials from the early universe till today and discuss the relation to the predictions of ΛCDM.