General Relativity & Quantum Cosmology

When two black holes merge, they 'ringdown' as they settle into a final Kerr black hole. The ringdown part of the gravitational wave signal probes the strong field gravity, enabling us to test the general theory of relativity (GR) in that regime. In this talk, I will focus on one particular challenge associated with the ringdown - "When does a ringdown start during a binary black hole merger?". Then I will end the talk with a brief summary of our prospects to perform GR tests with the ringdown signals using the current and future ground-based gravitational wave observatory.

The SYK model and its variants are a new class of large N conformal field theories. In this talk, we solve SYK, computing all connected correlation functions. Our techniques and results for summing all leading large N Feynman diagrams are applicable to a significantly broader class of theories. 

In general relativity causal relations between any pair of events is uniquely determined by locally predefined variables - the distribution of matter-energy degrees of freedom in the events' past light-cone. Under the assumption of locally predefined causal order, agents performing freely chosen local operations on an initially local quantum state cannot violate Bell inequalities. However, superposition of massive objects can effectively lead to "entanglement" in the temporal order between groups of local operations, enabling the violation of the inequalities. This shows that temporal orders between events can be "indefinite" in non-classical space-times.