Licentiate thesis defense: Gravitational collapse in bimetric gravity

Einstein’s theory of general relativity has been the prevailing theory of classical gravity for over a century. Its observational consistency is unparalleled. There are however a few (arguably) serious short-comings. First, the cosmological standard model, within which general relativity plays a crucial role, implies that the main part of the matter content of the universe is unknown (dark matter). Second, Einstein’s theory cannot be quantized and predicts singularities where the theory breaks down. Hence, there are strong reasons to consider extended theories of gravitation. Bimetric gravity is such a theory. Besides a massless spin-2 field, this theory exhibits a massive spin-2 field.

To be competitive, bimetric gravity should describe observational data at least as well as general relativity. Therefore, it is of uttermost importance to analyze the solutions to the equations of motion. In this licentiate thesis, we analyze gravitational collapse in spherical symmetry. We examine an exact solution where the matter content consists of massless and pressureless particles (dust). One of the main conclusions is that the end state is a Schwarzschild space-time which is also a solution to Einstein’s equations. Besides exact solutions, we perform numerical simulations of gravitational collapse in spherical symmetry. Starting with initial data close to a corresponding solution in general relativity, the evolution stays close and there is no evidence of a physical instability. We also investigate the role of symmetries and topology for bimetric gravity.