Gravitational radiation and black hole formation from gravitational collapse in theories of gravity with broken Lorentz symmetry.

Quantum gravity is expected to contain Lorentz symmetry only as an emergent low energy symmetry with the scale at which it is broken presently inaccessible to current experiments. My research, is centered around understanding various physical aspects of gravitational theories that modify general relativity by explicitly breaking Lorentz symmetry (i.e. Hořava-Lifshitz gravity and Einstein-æther theory) in gravitational sector, so that they are consistent with all current observations. In this dissertation I have studied numerically, gravitational collapse of a massless scalar field in Einstein-æther theory showing the existence of outermost “dynamical Universal horizons (dUHs)”. Such a dUH evolves into the causal boundary, even for excitations with arbitrarily large speeds of propagation. I have also studied the gravitational wave solutions in Einstein-æther theory and their behavior, especially how they may be potentially distinguishable by present or future detectors from the standard prediction of general relativity. I have also studied analytically black hole solutions in 2D Hořava gravity (non-projectable) which is non-minimally coupled with a nonrela-tivistic scalar field with focus on understanding Hawking radiation and the properties of the universal horizons.