General Relativity & Quantum Cosmology

We analyze the size of quantum gravity effects near black hole horizons. By considering black holes in asymptotically AdS spacetime, we can make use of the "quantum deviation" to estimate the size of quantum gravity corrections to the semiclassical analysis. We find that, in a typical pure state, corrections to correlation functions are typically of order exp(-S/2). Both the magnitude and time dependence of the correlator differ from previous results related to the spectral form factor, which estimated the correlator in a thermal state. Our results severely constrain proposals, such as non-violent unitarization and some versions of fuzzballs, that predict significant corrections to the semiclassical computation of correlation functions near black holes. We point out one possible loophole: our results rely on the standard result that bulk reconstruction is state independent for small perturbations outside the black hole.

With upcoming LIGO runs and new projects like LSST and ULTRASAT, black hole (BH)-powered multi-messenger events will be at the forefront of astrophysics. A major challenge in studying BH-powered explosions is the vast dynamical range between the BH and the emission site, which has hindered theoretical models from capturing the underlying physics from observations. Using 3D neutrino-general relativistic magnetohydrodynamic simulations, I will present the first such models, introducing an innovative model that now enables us to link GRB classes in mergers to their central engines and binary merger origins. For collapsing stars, I will demonstrate how our simulations open new frontiers in astrophysics, including a novel idea of how nascent BHs acquire their strong magnetic fields, heavy element nucleosynthesis in supernovae, the evolution of relativistic jets, new types of transients, and predictions of new vigorous, coherent, non-inspiral gravitational wave sources that may already be detectable by LIGO. These insights will be crucial for extracting the physics of transients from future gravitational wave and electromagnetic detections.

As endpoints of massive stellar evolution, showcases for the densest matter in the universe, and sites for heavy element nucleosynthesis, neutron star mergers are superb laboratories for astrophysics, strong gravity and nuclear physics. Gravitational-wave observations of these mergers are beginning to reveal neutron stars’ internal structure, provide insight into the astrophysical processes that form them, and expose their role in the chemical evolution of the Galaxy. I will survey some of my recent work in these areas and describe how our theoretical understanding of neutron stars is being shaped by gravitational-wave discoveries.

We will explore the connection between Celestial and Euclidean Anti-de Sitter (EAdS) holography in the massive scalar case. Specifically, exploiting the so-called hyperbolic foliation of Minkowski space-time, we will show that each contribution to massive Celestial correlators can be reformulated as a linear combination of contributions to corresponding massive Witten correlators in EAdS. This result will be demonstrated explicitly both for contact diagrams and for the four-point particle exchange diagram, and it extends to all orders in perturbation theory by leveraging the bootstrapping properties of the Celestial CFT (CCFT).  Within this framework, the Kantorovic-Lebedev transform plays a central role, which will be introduced at the end of the talk. This transform will allow us to make broader considerations regarding non-perturbative properties of a CCFT. 

In this talk, I will provide an overview of neutron star (NS) mergers, highlighting the insights gained through numerical relativity simulations. I will mainly focus on the role of the cocoon shock breakout emission as a key early electromagnetic counterpart of NS mergers, with special relevance to events like GW170817. I will explore how the properties of the merger ejecta and the nature of the central engine influence the resulting emission. Additionally, I will present recent advancements in the development of our new general relativistic magnetohydrodynamics (GR-MHD) code GR-Athena++, and share ongoing research efforts on the evolution of magnetic fields in the post-merger remnant.