General Relativity & Quantum Cosmology

In January 2024, the Laser Interferometer Space Antenna (LISA) mission was officially adopted by the European Space Agency, marking a new era in gravitational wave astronomy. LISA will be the first space-based gravitational wave detector, designed to explore the cosmos in the millihertz frequency range. This talk will present the mission's key scientific objectives and how the scientific community is preparing for the exploitation of LISA data. I will discuss the anticipated source types and the fundamental questions they could help answer. Then, we will focus on Extreme Mass Ratio Inspirals (EMRIs), a class of sources where small compact objects orbit the massive black holes at the centers of galaxies. These systems hold immense scientific potential for the LISA mission, as they encode a detailed map of the spacetime around the massive black hole. I will discuss how future detections of EMRIs can be used to constrain parameters related to accretion disks and modifications of General Relativity. Finally, I will highlight the path forward in preparing for LISA's launch and how to get involved in contributing to the mission scientific success. 

The Celestial Holography conjecture posits the existence of a codimension two theory whose correlators compute the S-matrix in a conformal primary basis. Although resembling a CFT in several respects, the intrinsic definition of this proposed dual theory remains elusive. In this talk, I will discuss a conjecture suggesting that Celestial CFT (CCFT) is related to a dimensionally reduced CFT on the Lorentzian cylinder and present some concrete examples of celestial amplitudes constructed in this way.

According to general relativity, the remnant of a binary black hole merger is a perturbed Kerr black hole. Perturbed Kerr black holes emit "ringdown" radiation which is well described by a superposition of damped exponentials ("quasinormal modes”), with frequencies and damping times that depend only on the mass and spin of the remnant. The observation of gravitational radiation emitted by black hole mergers might finally provide direct evidence of black holes, just like the 21 cm line identifies interstellar hydrogen. I will review the current status of this "black hole spectroscopy" program. I will focus on: (1) the role of nonlinearities in ringdown modeling, (2) the current observational status of black hole spectroscopy, and (3) future prospects for the observability of modified gravity effects and nonlinear modes.